Nobel Prize in Physics

Presentation Speech by Professor Gösta Ekspong of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen.

The Nobel Prize for Physics has been awarded to Dr. Georg Bednorz and Professor Dr. Alex Müller by the Royal Swedish Academy of Sciences “for their important breakthrough in the discovery of superconductivity in ceramic materials”. This discovery is quite recent – less than two years old – but it has already stimulated research and development throughout the world to an unprecedented extent. The discovery made by this year’s laureates concerns the transport of electricity without any resistance whatsoever and also the expulsion of magnetic flux from superconductors.

Common experience tells us that bodies in motion meet resistance in the form of friction. Sometimes this is useful, occasionally unwanted. One could save energy, that is to say fuel, by switching off the engine of a car when it had attained the desired speed, were it not for the breaking effect of friction. An electric current amounts to a traffic of a large number of electrons in a conductor. The electrons are compelled to elbow and jostle among the atoms which usually do not make room without resistance. As a consequence some energy is converted into heat. Sometimes the heat is desirable as in a hot plate or a toaster, occasionally it is undesirable as when electric power is produced and distributed and when it is used in electromagnets, in computers and in many other devices.

The Dutch scientist Heike Kamerlingh-Onnes was awarded the Nobel Prize for Physics in 1913. Two years earlier he had discovered a new remarkable phenomenon, namely that the electric resistance of solid mercury could completely disappear. Superconductivity, as the phenomenon is called, has been shown to occur in some other metals and alloys.

Why hasn’t such an energy saving property already been extensively applied? The answer is, that this phenomenon appears only at very low temperatures; in the case of mercury at -269 degrees Celsius, which means 4 degrees above the absolute zero. Superconductivity at somewhat higher temperatures has been found in certain alloys. However, in the 1970’s progress seemed to halt at about 23 degrees above the absolute zero. It is not possible to reach this kind of temperatures without effort and expense. The dream of achieving the transport of electricity without energy losses has been realized only in special cases.

Another remarkable phenomenon appears when a material during cooling crosses the temperature boundary for superconductivity. The field of a nearby magnet is expelled from the superconductor with such force that the magnet can become levitated and remain floating in the air. However, the dream of frictionless trains based on levitated magnets has not been realisable on a large scale because of the difficulties with the necessarily low temperatures.

Dr. Bednorz and Professor Müller started some years ago a search for superconductivity in materials other than the usual alloys. Their new approach met with success early last year, when they found a sudden drop towards zero resistance in a ceramic material consisting of lanthanum-barium-copper oxide. Sensationally, the boundary temperature was 50 % higher than ever before, as measured from absolute zero. The expulsion of magnetic flux, which is a sure mark of superconductivity, was shown to occur in a following publication.

When other experts had overcome their scientifically trained sceptiscism and had carried out their own control experiments, a large number of scientists decided to enter the new line of research. New ceramic materials were synthesized with superconductivity at temperatures such that the cooling suddenly became a simple operation. New results from all over the world flooded the international scientific journals, which found difficulties in coping with the situation. Research councils, industries and politicians are busily considering means to best promote the not so easy development work in order to benefit from the promising possibilities now in sight.

Scientists strive to describe in detail how the absence of resistance to the traffic of electrons is possible and to find the traffic rules, i. e. the laws of nature, which apply. The trio of John Bardeen, Leon Cooper and Robert Schrieffer found the solution 30 years ago in the case of the older types of superconductors and were awarded the Nobel Prize for Physics in 1972. Superconductivity in the new materials has reopened and revitalized the scientific debate in this field.

Herr Dr Bednorz und Herr Professor Müller:

In Ihren bahnbrechenden Arbeiten haben Sic einen neuen, sehr erfolgreichen Weg fir die Erforschung und die Entwicklung der Supraleitung angegeben. Sehr viele Wissenschaftler hohen Ranges sind zurzeit auf dem Gebiet tätig, das Sie eröffnet haben.

Mir ist die Aufgabe zugefallen, Ihnen die herzlichsten Glückwünsche der Küniglich Schwedischen Akademie der Wissenschaften zu übermitteln. Darf ich Sie nun bitten vorzutreten um Ihren Preis aus der Hand Seiner Majestät des Königs entgegenzunehmen.

Presentation Speech by Professor Gösta Ekspong of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen.

The Nobel Prize for Physics has been awarded to Dr. Georg Bednorz and Professor Dr. Alex Müller by the Royal Swedish Academy of Sciences “for their important breakthrough in the discovery of superconductivity in ceramic materials”. This discovery is quite recent – less than two years old – but it has already stimulated research and development throughout the world to an unprecedented extent. The discovery made by this year’s laureates concerns the transport of electricity without any resistance whatsoever and also the expulsion of magnetic flux from superconductors.

Common experience tells us that bodies in motion meet resistance in the form of friction. Sometimes this is useful, occasionally unwanted. One could save energy, that is to say fuel, by switching off the engine of a car when it had attained the desired speed, were it not for the breaking effect of friction. An electric current amounts to a traffic of a large number of electrons in a conductor. The electrons are compelled to elbow and jostle among the atoms which usually do not make room without resistance. As a consequence some energy is converted into heat. Sometimes the heat is desirable as in a hot plate or a toaster, occasionally it is undesirable as when electric power is produced and distributed and when it is used in electromagnets, in computers and in many other devices.

The Dutch scientist Heike Kamerlingh-Onnes was awarded the Nobel Prize for Physics in 1913. Two years earlier he had discovered a new remarkable phenomenon, namely that the electric resistance of solid mercury could completely disappear. Superconductivity, as the phenomenon is called, has been shown to occur in some other metals and alloys.

Why hasn’t such an energy saving property already been extensively applied? The answer is, that this phenomenon appears only at very low temperatures; in the case of mercury at -269 degrees Celsius, which means 4 degrees above the absolute zero. Superconductivity at somewhat higher temperatures has been found in certain alloys. However, in the 1970’s progress seemed to halt at about 23 degrees above the absolute zero. It is not possible to reach this kind of temperatures without effort and expense. The dream of achieving the transport of electricity without energy losses has been realized only in special cases.

Another remarkable phenomenon appears when a material during cooling crosses the temperature boundary for superconductivity. The field of a nearby magnet is expelled from the superconductor with such force that the magnet can become levitated and remain floating in the air. However, the dream of frictionless trains based on levitated magnets has not been realisable on a large scale because of the difficulties with the necessarily low temperatures.

Dr. Bednorz and Professor Müller started some years ago a search for superconductivity in materials other than the usual alloys. Their new approach met with success early last year, when they found a sudden drop towards zero resistance in a ceramic material consisting of lanthanum-barium-copper oxide. Sensationally, the boundary temperature was 50 % higher than ever before, as measured from absolute zero. The expulsion of magnetic flux, which is a sure mark of superconductivity, was shown to occur in a following publication.

When other experts had overcome their scientifically trained sceptiscism and had carried out their own control experiments, a large number of scientists decided to enter the new line of research. New ceramic materials were synthesized with superconductivity at temperatures such that the cooling suddenly became a simple operation. New results from all over the world flooded the international scientific journals, which found difficulties in coping with the situation. Research councils, industries and politicians are busily considering means to best promote the not so easy development work in order to benefit from the promising possibilities now in sight.

Scientists strive to describe in detail how the absence of resistance to the traffic of electrons is possible and to find the traffic rules, i. e. the laws of nature, which apply. The trio of John Bardeen, Leon Cooper and Robert Schrieffer found the solution 30 years ago in the case of the older types of superconductors and were awarded the Nobel Prize for Physics in 1972. Superconductivity in the new materials has reopened and revitalized the scientific debate in this field.

Herr Dr Bednorz und Herr Professor Müller:

In Ihren bahnbrechenden Arbeiten haben Sic einen neuen, sehr erfolgreichen Weg fir die Erforschung und die Entwicklung der Supraleitung angegeben. Sehr viele Wissenschaftler hohen Ranges sind zurzeit auf dem Gebiet tätig, das Sie eröffnet haben.

Mir ist die Aufgabe zugefallen, Ihnen die herzlichsten Glückwünsche der Küniglich Schwedischen Akademie der Wissenschaften zu übermitteln. Darf ich Sie nun bitten vorzutreten um Ihren Preis aus der Hand Seiner Majestät des Königs entgegenzunehmen.

Presentation Speech by Professor Lamek Hulthén of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

This year’s prize is shared between Peter Leonidovitj Kapitza, Moscow, “for his basic inventions and discoveries in the area of low-temperature physics” and Arno A. Penzias and Robert W. Wilson, Holmdel, New Jersey, USA, “for their discovery of cosmic microwave background radiation”.

By low temperatures we mean temperatures just above the absolute zero, -273°C, where all heat motion ceases and no gases can exist. It is handy to count degrees from this zero point: “degrees Kelvin” (after the British physicist Lord Kelvin) E.g. 3 K (K = Kelvin) means the same as -270°C.

Seventy years ago the Dutch physicist Kamerlingh-Onnes succeeded in liquefying helium, starting a development that revealed many new and unexpected phenomena. In 1911 he discovered superconductivity in mercury: the electric resistance disappeared completely at about 4 K. 1913 Kamerlingh-Onnes received the Nobel prize in physics for his discoveries, and his laboratory in Leiden ranked for many years as the Mekka of low temperature physics, to which also many Swedish scholars went on pilgrimage.

In the late twenties the Leiden workers got a worthy competitor in the young Russian Kapitza, then working with Rutherford in Cambridge, England. His achievements made such an impression that a special institute was created for him: the Royal Society Mond Laboratory (named after the donor Mond), where he stayed until 1934. Foremost among his works from this period stands an ingenious device for liquefying helium in large quantities – a pre-requisite for the great progress made in low temperature physics during the last quarter-century.

Back in his native country Kapitza had to build up a new institute from scratch. Nevertheless, in 1938 he surprised the physics community by the discovery of the superfluidity of helium, implying that the internal friction (viscosity) of the fluid disappears below 2.2 K (the so-called lambda-point of helium). The same discovery was made independently by Allen and Misener at the Mond Laboratory. Later Kapitza has pursued these investigations in a brilliant way, at the same time guiding and inspiring younger collaborators, among whom we remember the late Lev Landau, recipient of the physics prize 1962 “for his pioneering theories for condensed matter, especially liquid helium”. Among Kapitza’s accomplishments we should also mention the method he developed for producing very strong magnetic fields.

Kapitza stands out as one of the greatest experimenters of our time, in his domain the uncontested pioneer, leader and master.

We now move from the Institute of Physical Problems, Moscow, to Bell Telephone Laboratories, Holmdel, New Jersey, USA. Here Karl Jansky, in the beginning of the thirties, built a large movable aerial to investigate sources of radio noise and discovered that some of the noise was due to radio waves coming from the Milky Way. This was the beginning of radio astronomy that has taken such an astounding development after the second World War – as an illustration let me recall the discovery of the pulsars, honoured with the physics prize 1974.

In the early 1960ies a station was set up in Holmdel to communicate with the satellites Echo and Telstar. The equipment, including a steerable horn antenna, made it a very sensitive receiver for microwaves, i.e. radio waves of a few cm wavelength. Later radio astronomers Arno Penzias and Robert Wilson got the chance to adapt the instrument for observing radio noise e.g. from the Milky Way. They chose a wave length c. 7 cm where the cosmic contribution was supposed to be insignificant. The task of eliminating various sources of errors and noise turned out to be very difficult and time-consuming, but by and by it became clear that they had found a background radiation, equally strong in all directions, independent of time of the day and the year, so it could not come from the sun or our Galaxy. The strength of the radiation corresponded to what technicians call an antenna temperature of 3 K.

Continued investigations have confirmed that this background radiation varies with wave length in the way prescribed by wellknown laws for a space, kept at the temperature 3 K. Our Italian colleagues call it “la luce fredda” – the cold light.

But where does the cold light come from? A possible explanation was given by Princeton physicists Dicke, Peebles, Roll and Wilkinson and published together with the report of Penzias and Wilson. It leans on a cosmological theory, developed about 30 years ago by the Russian born physicist George Gamow and his collaborators Alpher and Herman. Starting from the fact that the universe is now expanding uniformly, they concluded that it must have been very compact about 15 billion years ago and ventured to assume that the universe was born in a huge explosionthe “Big Bang”. The temperature must then have been fabulous: 10 billion degrees, perhaps more. At such temperatures lighter chemical elements can be formed from existing elementary particles, and a tremendous amount of radiation of all wave lengths is released. In the ensuing expansion of the universe, the temperature of the radiation rapidly goes down. Alpher and Herman estimated that this radiation would still be left with a temperature around 5 K. At that time, however, it was considered out of the question, that such a radiation would ever be possible to observe. For this and other reasons the predictions were forgotten.

Have Penzias and Wilson discovered “the cold light from the birth of the universe”? It is possible – this much is certain that their exceptional perseverance and skill in the experiments led them to a discovery, after which cosmology is a science, open to verification by experiment and observation.

Piotr Kapitsa, Arno Penzias, Robert Wilson, In accordance with our tradition I have given a brief account in Swedish of the achievements, for which you share this year’s Nobel prize in Physics. It is my privilege and pleasure to congratulate you on behalf of the Royal Swedish Academy of Sciences and ask you to receive your prizes from the hands of His Majesty the King!

Presentation Speech by Professor Lamek Hulthén of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

This year’s prize is shared between Peter Leonidovitj Kapitza, Moscow, “for his basic inventions and discoveries in the area of low-temperature physics” and Arno A. Penzias and Robert W. Wilson, Holmdel, New Jersey, USA, “for their discovery of cosmic microwave background radiation”.

By low temperatures we mean temperatures just above the absolute zero, -273°C, where all heat motion ceases and no gases can exist. It is handy to count degrees from this zero point: “degrees Kelvin” (after the British physicist Lord Kelvin) E.g. 3 K (K = Kelvin) means the same as -270°C.

Seventy years ago the Dutch physicist Kamerlingh-Onnes succeeded in liquefying helium, starting a development that revealed many new and unexpected phenomena. In 1911 he discovered superconductivity in mercury: the electric resistance disappeared completely at about 4 K. 1913 Kamerlingh-Onnes received the Nobel prize in physics for his discoveries, and his laboratory in Leiden ranked for many years as the Mekka of low temperature physics, to which also many Swedish scholars went on pilgrimage.

In the late twenties the Leiden workers got a worthy competitor in the young Russian Kapitza, then working with Rutherford in Cambridge, England. His achievements made such an impression that a special institute was created for him: the Royal Society Mond Laboratory (named after the donor Mond), where he stayed until 1934. Foremost among his works from this period stands an ingenious device for liquefying helium in large quantities – a pre-requisite for the great progress made in low temperature physics during the last quarter-century.

Back in his native country Kapitza had to build up a new institute from scratch. Nevertheless, in 1938 he surprised the physics community by the discovery of the superfluidity of helium, implying that the internal friction (viscosity) of the fluid disappears below 2.2 K (the so-called lambda-point of helium). The same discovery was made independently by Allen and Misener at the Mond Laboratory. Later Kapitza has pursued these investigations in a brilliant way, at the same time guiding and inspiring younger collaborators, among whom we remember the late Lev Landau, recipient of the physics prize 1962 “for his pioneering theories for condensed matter, especially liquid helium”. Among Kapitza’s accomplishments we should also mention the method he developed for producing very strong magnetic fields.

Kapitza stands out as one of the greatest experimenters of our time, in his domain the uncontested pioneer, leader and master.

We now move from the Institute of Physical Problems, Moscow, to Bell Telephone Laboratories, Holmdel, New Jersey, USA. Here Karl Jansky, in the beginning of the thirties, built a large movable aerial to investigate sources of radio noise and discovered that some of the noise was due to radio waves coming from the Milky Way. This was the beginning of radio astronomy that has taken such an astounding development after the second World War – as an illustration let me recall the discovery of the pulsars, honoured with the physics prize 1974.

In the early 1960ies a station was set up in Holmdel to communicate with the satellites Echo and Telstar. The equipment, including a steerable horn antenna, made it a very sensitive receiver for microwaves, i.e. radio waves of a few cm wavelength. Later radio astronomers Arno Penzias and Robert Wilson got the chance to adapt the instrument for observing radio noise e.g. from the Milky Way. They chose a wave length c. 7 cm where the cosmic contribution was supposed to be insignificant. The task of eliminating various sources of errors and noise turned out to be very difficult and time-consuming, but by and by it became clear that they had found a background radiation, equally strong in all directions, independent of time of the day and the year, so it could not come from the sun or our Galaxy. The strength of the radiation corresponded to what technicians call an antenna temperature of 3 K.

Continued investigations have confirmed that this background radiation varies with wave length in the way prescribed by wellknown laws for a space, kept at the temperature 3 K. Our Italian colleagues call it “la luce fredda” – the cold light.

But where does the cold light come from? A possible explanation was given by Princeton physicists Dicke, Peebles, Roll and Wilkinson and published together with the report of Penzias and Wilson. It leans on a cosmological theory, developed about 30 years ago by the Russian born physicist George Gamow and his collaborators Alpher and Herman. Starting from the fact that the universe is now expanding uniformly, they concluded that it must have been very compact about 15 billion years ago and ventured to assume that the universe was born in a huge explosionthe “Big Bang”. The temperature must then have been fabulous: 10 billion degrees, perhaps more. At such temperatures lighter chemical elements can be formed from existing elementary particles, and a tremendous amount of radiation of all wave lengths is released. In the ensuing expansion of the universe, the temperature of the radiation rapidly goes down. Alpher and Herman estimated that this radiation would still be left with a temperature around 5 K. At that time, however, it was considered out of the question, that such a radiation would ever be possible to observe. For this and other reasons the predictions were forgotten.

Have Penzias and Wilson discovered “the cold light from the birth of the universe”? It is possible – this much is certain that their exceptional perseverance and skill in the experiments led them to a discovery, after which cosmology is a science, open to verification by experiment and observation.

Piotr Kapitsa, Arno Penzias, Robert Wilson, In accordance with our tradition I have given a brief account in Swedish of the achievements, for which you share this year’s Nobel prize in Physics. It is my privilege and pleasure to congratulate you on behalf of the Royal Swedish Academy of Sciences and ask you to receive your prizes from the hands of His Majesty the King!

Presentation Speech by Professor Lamek Hulthén of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

This year’s prize is shared between Peter Leonidovitj Kapitza, Moscow, “for his basic inventions and discoveries in the area of low-temperature physics” and Arno A. Penzias and Robert W. Wilson, Holmdel, New Jersey, USA, “for their discovery of cosmic microwave background radiation”.

By low temperatures we mean temperatures just above the absolute zero, -273°C, where all heat motion ceases and no gases can exist. It is handy to count degrees from this zero point: “degrees Kelvin” (after the British physicist Lord Kelvin) E.g. 3 K (K = Kelvin) means the same as -270°C.

Seventy years ago the Dutch physicist Kamerlingh-Onnes succeeded in liquefying helium, starting a development that revealed many new and unexpected phenomena. In 1911 he discovered superconductivity in mercury: the electric resistance disappeared completely at about 4 K. 1913 Kamerlingh-Onnes received the Nobel prize in physics for his discoveries, and his laboratory in Leiden ranked for many years as the Mekka of low temperature physics, to which also many Swedish scholars went on pilgrimage.

In the late twenties the Leiden workers got a worthy competitor in the young Russian Kapitza, then working with Rutherford in Cambridge, England. His achievements made such an impression that a special institute was created for him: the Royal Society Mond Laboratory (named after the donor Mond), where he stayed until 1934. Foremost among his works from this period stands an ingenious device for liquefying helium in large quantities – a pre-requisite for the great progress made in low temperature physics during the last quarter-century.

Back in his native country Kapitza had to build up a new institute from scratch. Nevertheless, in 1938 he surprised the physics community by the discovery of the superfluidity of helium, implying that the internal friction (viscosity) of the fluid disappears below 2.2 K (the so-called lambda-point of helium). The same discovery was made independently by Allen and Misener at the Mond Laboratory. Later Kapitza has pursued these investigations in a brilliant way, at the same time guiding and inspiring younger collaborators, among whom we remember the late Lev Landau, recipient of the physics prize 1962 “for his pioneering theories for condensed matter, especially liquid helium”. Among Kapitza’s accomplishments we should also mention the method he developed for producing very strong magnetic fields.

Kapitza stands out as one of the greatest experimenters of our time, in his domain the uncontested pioneer, leader and master.

We now move from the Institute of Physical Problems, Moscow, to Bell Telephone Laboratories, Holmdel, New Jersey, USA. Here Karl Jansky, in the beginning of the thirties, built a large movable aerial to investigate sources of radio noise and discovered that some of the noise was due to radio waves coming from the Milky Way. This was the beginning of radio astronomy that has taken such an astounding development after the second World War – as an illustration let me recall the discovery of the pulsars, honoured with the physics prize 1974.

In the early 1960ies a station was set up in Holmdel to communicate with the satellites Echo and Telstar. The equipment, including a steerable horn antenna, made it a very sensitive receiver for microwaves, i.e. radio waves of a few cm wavelength. Later radio astronomers Arno Penzias and Robert Wilson got the chance to adapt the instrument for observing radio noise e.g. from the Milky Way. They chose a wave length c. 7 cm where the cosmic contribution was supposed to be insignificant. The task of eliminating various sources of errors and noise turned out to be very difficult and time-consuming, but by and by it became clear that they had found a background radiation, equally strong in all directions, independent of time of the day and the year, so it could not come from the sun or our Galaxy. The strength of the radiation corresponded to what technicians call an antenna temperature of 3 K.

Continued investigations have confirmed that this background radiation varies with wave length in the way prescribed by wellknown laws for a space, kept at the temperature 3 K. Our Italian colleagues call it “la luce fredda” – the cold light.

But where does the cold light come from? A possible explanation was given by Princeton physicists Dicke, Peebles, Roll and Wilkinson and published together with the report of Penzias and Wilson. It leans on a cosmological theory, developed about 30 years ago by the Russian born physicist George Gamow and his collaborators Alpher and Herman. Starting from the fact that the universe is now expanding uniformly, they concluded that it must have been very compact about 15 billion years ago and ventured to assume that the universe was born in a huge explosionthe “Big Bang”. The temperature must then have been fabulous: 10 billion degrees, perhaps more. At such temperatures lighter chemical elements can be formed from existing elementary particles, and a tremendous amount of radiation of all wave lengths is released. In the ensuing expansion of the universe, the temperature of the radiation rapidly goes down. Alpher and Herman estimated that this radiation would still be left with a temperature around 5 K. At that time, however, it was considered out of the question, that such a radiation would ever be possible to observe. For this and other reasons the predictions were forgotten.

Have Penzias and Wilson discovered “the cold light from the birth of the universe”? It is possible – this much is certain that their exceptional perseverance and skill in the experiments led them to a discovery, after which cosmology is a science, open to verification by experiment and observation.

Piotr Kapitsa, Arno Penzias, Robert Wilson, In accordance with our tradition I have given a brief account in Swedish of the achievements, for which you share this year’s Nobel prize in Physics. It is my privilege and pleasure to congratulate you on behalf of the Royal Swedish Academy of Sciences and ask you to receive your prizes from the hands of His Majesty the King!

Presentation Speech by professor Stig Lundqvist of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesty, Your Royal Highnesses, Ladies and Gentlemen,

The 1973 Nobel Prize for physics has been awarded to Drs. Leo Esaki, Ivar Giaever and Brian Josephson for their discoveries of tunnelling phenomena in solids.

The tunnelling phenomena belong to the most direct consequences of the laws of modern physics and have no analogy in classical mechanics. Elementary particles such as electrons cannot be treated as classical particles but show both wave and particle properties. Electrons are described mathematically by the solutions of a wave equation, the Schrödinger equation. An electron and its motion can be described by a superposition of simple waves, which forms a wave packet with a finite extension in space. The waves can penetrate a thin barrier, which would be a forbidden region if we treat the electron as a classical particle. The term tunnelling refers to this wave-like property – the particle “tunnels” through the forbidden region. In order to get a notion of this kind of phenomenon let us assume that you are throwing balls against a wall. In general the ball bounces back but occasionally the ball disappears straight through the wall. In principle this could happen, but the probability for such an event is negligibly small.

On the atomic level, on the other hand, tunnelling is a rather common phenomenon. Let us instead of balls consider electrons in a metal moving with high velocities towards a forbidden region, for example a thin insulating barrier. In this case we cannot neglect the probability of tunneling. A certain fraction of the electrons will penetrate the barrier by tunnelling and we may obtain a weak tunnel current through the barrier.

The interest for tunnelling phenomena goes back to the early years of quantum mechanics, i.e. the late twenties. The best known early application of the ideas came in the model of alpha-decay of heavy atomic nuclei. Some phenomena in solids were explained by tunnelling in the early years. However, theory and experiments often gave conflicting results, no further progress was made and physicists lost interest in solid state tunnelling in the early thirties.

With the discovery of the transistor effect in 1947 came a renewed interest in the tunnelling process. Many attempts were made to observe tunnelling in semiconductors, but the results were controversial and inconclusive.

It was the young Japanese physicist Leo Esaki, who made the initial pioneering discovery that opened the field of tunnelling phenomena for research. He was at the time with the Sony Corporation, where he performed some deceptively simple experiments, which gave convincing experimental evidence for tunnelling of electrons in solids, a phenomenon which had been clouded by questions for decades. Not only was the existence of tunnelling in semiconductors established, but he also showed and explained an unforeseen aspect of tunnelling in semiconductor junctions. This new aspect led to the development of an important device, called the tunnel diode or the Esaki diode.

Esaki’s discovery, published in 1958, opened a new field of research based on tunnelling in semiconductors. The method soon became of great importance in solid state physics because of its simplicity in principle and the high sensitivity of tunnelling to many finer details.

The next major advance in the field of tunnelling came in the field of superconductivity through the work of Ivar Giaever in 1960. In 1957, Bardeen, Cooper and Schrieffer had published their theory of superconductivity, which was awarded the 1972 Nobel Prize in physics. A crucial part of their theory is that an energy gap appears in the electron spectrum when a metal becomes superconducting. Giaever speculated that the energy gap should be reflected in the current-voltage relation in a tunnelling experiment. He studied tunnelling of electrons through a thin sandwich of evaporated metal films insulated by the natural oxide of the film first evaporated. The experiments showed that his conjecture was correct and his tunnelling method soon became the dominating method to study the energy gap in superconductors. Giaever also observed a characteristic fine structure in the tunnel current, which depends on the coupling of the electrons to the vibrations of the lattice. Through later work by Giaever and others the tunnelling method has developed into a new spectroscopy of high accuracy to study in detail the properties of superconductors, and the experiments have in a striking way confirmed the validity of the theory of superconductivity.

Giaver’s experiments left certain theoretical questions open and this inspired the young Brian Josephson to make a penetrating theoretical analysis of tunnelling between two superconductors. In addition to the Giaever current he found a weak current due to tunelling of coupled electron pairs, called Coopers pairs. This implies that we get a supercurrent through the barrier. He predicted two remarkable effects. The first effect is that a supercurrent may flow even if no voltage is applied. The second effect is that a high frequency alternating current will pass through the barrier if a constant voltage is applied.

Josephson’s theoretical discoveries showed how one can influence supercurrents by applying electric and magnetic fields and thereby control, study and exploit quantum phenomena on a macroscopic scale. His discoveries have led to the development of an entirely new method called quantum interferometry. This method has led to the development of a rich variety of instruments of extraordinary sensitivity and precision with application in wide areas of science and technology.

Esaki, Giaever and Josephson have through their discoveries opened up new fields of research in physics. They are closely related because the pioneering work by Esaki provided the foundation and direct impetus for Giaever’s discovery and Giaever’s work in turn provided the stimulus which led to Jo- sephson’s theoretical predictions. The close relation between the abstract concepts and sophisticated tools of modern physics and the practical applications to science and technology is strongly emphasized in these discoveries. The applications of solid state tunnelling already cover a wide range. Many devices based on tunneling are now used in electronics. The new quantum interferometry has already been used in such different applications as measurements of temperatures near the absolute zero, to detect gravitational waves, for ore prospecting, for communication through water and through mountains, to study the electromagnetic field around the heart or brain, to mention a few examples.

Drs. Esaki, Giaever and Josephson,

In a series of brilliant experiments and calculations you have explored different aspects of tunelling phenomena in solids. Your discoveries have opened up new fields of research and have given new fundamental insight about electrons in semiconductors and superconductors and about macroscopic quantum phenomena in superconductors.

On behalf of the Royal Academy of Sciences I wish to express our admiration and convey to you our warmest congratulations. I now ask you to proceed to receive your prizes from the hands of his Majesty the King.

Presentation Speech by professor Stig Lundqvist of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesty, Your Royal Highnesses, Ladies and Gentlemen,

The 1973 Nobel Prize for physics has been awarded to Drs. Leo Esaki, Ivar Giaever and Brian Josephson for their discoveries of tunnelling phenomena in solids.

The tunnelling phenomena belong to the most direct consequences of the laws of modern physics and have no analogy in classical mechanics. Elementary particles such as electrons cannot be treated as classical particles but show both wave and particle properties. Electrons are described mathematically by the solutions of a wave equation, the Schrödinger equation. An electron and its motion can be described by a superposition of simple waves, which forms a wave packet with a finite extension in space. The waves can penetrate a thin barrier, which would be a forbidden region if we treat the electron as a classical particle. The term tunnelling refers to this wave-like property – the particle “tunnels” through the forbidden region. In order to get a notion of this kind of phenomenon let us assume that you are throwing balls against a wall. In general the ball bounces back but occasionally the ball disappears straight through the wall. In principle this could happen, but the probability for such an event is negligibly small.

On the atomic level, on the other hand, tunnelling is a rather common phenomenon. Let us instead of balls consider electrons in a metal moving with high velocities towards a forbidden region, for example a thin insulating barrier. In this case we cannot neglect the probability of tunneling. A certain fraction of the electrons will penetrate the barrier by tunnelling and we may obtain a weak tunnel current through the barrier.

The interest for tunnelling phenomena goes back to the early years of quantum mechanics, i.e. the late twenties. The best known early application of the ideas came in the model of alpha-decay of heavy atomic nuclei. Some phenomena in solids were explained by tunnelling in the early years. However, theory and experiments often gave conflicting results, no further progress was made and physicists lost interest in solid state tunnelling in the early thirties.

With the discovery of the transistor effect in 1947 came a renewed interest in the tunnelling process. Many attempts were made to observe tunnelling in semiconductors, but the results were controversial and inconclusive.

It was the young Japanese physicist Leo Esaki, who made the initial pioneering discovery that opened the field of tunnelling phenomena for research. He was at the time with the Sony Corporation, where he performed some deceptively simple experiments, which gave convincing experimental evidence for tunnelling of electrons in solids, a phenomenon which had been clouded by questions for decades. Not only was the existence of tunnelling in semiconductors established, but he also showed and explained an unforeseen aspect of tunnelling in semiconductor junctions. This new aspect led to the development of an important device, called the tunnel diode or the Esaki diode.

Esaki’s discovery, published in 1958, opened a new field of research based on tunnelling in semiconductors. The method soon became of great importance in solid state physics because of its simplicity in principle and the high sensitivity of tunnelling to many finer details.

The next major advance in the field of tunnelling came in the field of superconductivity through the work of Ivar Giaever in 1960. In 1957, Bardeen, Cooper and Schrieffer had published their theory of superconductivity, which was awarded the 1972 Nobel Prize in physics. A crucial part of their theory is that an energy gap appears in the electron spectrum when a metal becomes superconducting. Giaever speculated that the energy gap should be reflected in the current-voltage relation in a tunnelling experiment. He studied tunnelling of electrons through a thin sandwich of evaporated metal films insulated by the natural oxide of the film first evaporated. The experiments showed that his conjecture was correct and his tunnelling method soon became the dominating method to study the energy gap in superconductors. Giaever also observed a characteristic fine structure in the tunnel current, which depends on the coupling of the electrons to the vibrations of the lattice. Through later work by Giaever and others the tunnelling method has developed into a new spectroscopy of high accuracy to study in detail the properties of superconductors, and the experiments have in a striking way confirmed the validity of the theory of superconductivity.

Giaver’s experiments left certain theoretical questions open and this inspired the young Brian Josephson to make a penetrating theoretical analysis of tunnelling between two superconductors. In addition to the Giaever current he found a weak current due to tunelling of coupled electron pairs, called Coopers pairs. This implies that we get a supercurrent through the barrier. He predicted two remarkable effects. The first effect is that a supercurrent may flow even if no voltage is applied. The second effect is that a high frequency alternating current will pass through the barrier if a constant voltage is applied.

Josephson’s theoretical discoveries showed how one can influence supercurrents by applying electric and magnetic fields and thereby control, study and exploit quantum phenomena on a macroscopic scale. His discoveries have led to the development of an entirely new method called quantum interferometry. This method has led to the development of a rich variety of instruments of extraordinary sensitivity and precision with application in wide areas of science and technology.

Esaki, Giaever and Josephson have through their discoveries opened up new fields of research in physics. They are closely related because the pioneering work by Esaki provided the foundation and direct impetus for Giaever’s discovery and Giaever’s work in turn provided the stimulus which led to Jo- sephson’s theoretical predictions. The close relation between the abstract concepts and sophisticated tools of modern physics and the practical applications to science and technology is strongly emphasized in these discoveries. The applications of solid state tunnelling already cover a wide range. Many devices based on tunneling are now used in electronics. The new quantum interferometry has already been used in such different applications as measurements of temperatures near the absolute zero, to detect gravitational waves, for ore prospecting, for communication through water and through mountains, to study the electromagnetic field around the heart or brain, to mention a few examples.

Drs. Esaki, Giaever and Josephson,

In a series of brilliant experiments and calculations you have explored different aspects of tunelling phenomena in solids. Your discoveries have opened up new fields of research and have given new fundamental insight about electrons in semiconductors and superconductors and about macroscopic quantum phenomena in superconductors.

On behalf of the Royal Academy of Sciences I wish to express our admiration and convey to you our warmest congratulations. I now ask you to proceed to receive your prizes from the hands of his Majesty the King.

Presentation Speech by professor Stig Lundqvist of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesty, Your Royal Highnesses, Ladies and Gentlemen,

The 1973 Nobel Prize for physics has been awarded to Drs. Leo Esaki, Ivar Giaever and Brian Josephson for their discoveries of tunnelling phenomena in solids.

The tunnelling phenomena belong to the most direct consequences of the laws of modern physics and have no analogy in classical mechanics. Elementary particles such as electrons cannot be treated as classical particles but show both wave and particle properties. Electrons are described mathematically by the solutions of a wave equation, the Schrödinger equation. An electron and its motion can be described by a superposition of simple waves, which forms a wave packet with a finite extension in space. The waves can penetrate a thin barrier, which would be a forbidden region if we treat the electron as a classical particle. The term tunnelling refers to this wave-like property – the particle “tunnels” through the forbidden region. In order to get a notion of this kind of phenomenon let us assume that you are throwing balls against a wall. In general the ball bounces back but occasionally the ball disappears straight through the wall. In principle this could happen, but the probability for such an event is negligibly small.

On the atomic level, on the other hand, tunnelling is a rather common phenomenon. Let us instead of balls consider electrons in a metal moving with high velocities towards a forbidden region, for example a thin insulating barrier. In this case we cannot neglect the probability of tunneling. A certain fraction of the electrons will penetrate the barrier by tunnelling and we may obtain a weak tunnel current through the barrier.

The interest for tunnelling phenomena goes back to the early years of quantum mechanics, i.e. the late twenties. The best known early application of the ideas came in the model of alpha-decay of heavy atomic nuclei. Some phenomena in solids were explained by tunnelling in the early years. However, theory and experiments often gave conflicting results, no further progress was made and physicists lost interest in solid state tunnelling in the early thirties.

With the discovery of the transistor effect in 1947 came a renewed interest in the tunnelling process. Many attempts were made to observe tunnelling in semiconductors, but the results were controversial and inconclusive.

It was the young Japanese physicist Leo Esaki, who made the initial pioneering discovery that opened the field of tunnelling phenomena for research. He was at the time with the Sony Corporation, where he performed some deceptively simple experiments, which gave convincing experimental evidence for tunnelling of electrons in solids, a phenomenon which had been clouded by questions for decades. Not only was the existence of tunnelling in semiconductors established, but he also showed and explained an unforeseen aspect of tunnelling in semiconductor junctions. This new aspect led to the development of an important device, called the tunnel diode or the Esaki diode.

Esaki’s discovery, published in 1958, opened a new field of research based on tunnelling in semiconductors. The method soon became of great importance in solid state physics because of its simplicity in principle and the high sensitivity of tunnelling to many finer details.

The next major advance in the field of tunnelling came in the field of superconductivity through the work of Ivar Giaever in 1960. In 1957, Bardeen, Cooper and Schrieffer had published their theory of superconductivity, which was awarded the 1972 Nobel Prize in physics. A crucial part of their theory is that an energy gap appears in the electron spectrum when a metal becomes superconducting. Giaever speculated that the energy gap should be reflected in the current-voltage relation in a tunnelling experiment. He studied tunnelling of electrons through a thin sandwich of evaporated metal films insulated by the natural oxide of the film first evaporated. The experiments showed that his conjecture was correct and his tunnelling method soon became the dominating method to study the energy gap in superconductors. Giaever also observed a characteristic fine structure in the tunnel current, which depends on the coupling of the electrons to the vibrations of the lattice. Through later work by Giaever and others the tunnelling method has developed into a new spectroscopy of high accuracy to study in detail the properties of superconductors, and the experiments have in a striking way confirmed the validity of the theory of superconductivity.

Giaver’s experiments left certain theoretical questions open and this inspired the young Brian Josephson to make a penetrating theoretical analysis of tunnelling between two superconductors. In addition to the Giaever current he found a weak current due to tunelling of coupled electron pairs, called Coopers pairs. This implies that we get a supercurrent through the barrier. He predicted two remarkable effects. The first effect is that a supercurrent may flow even if no voltage is applied. The second effect is that a high frequency alternating current will pass through the barrier if a constant voltage is applied.

Josephson’s theoretical discoveries showed how one can influence supercurrents by applying electric and magnetic fields and thereby control, study and exploit quantum phenomena on a macroscopic scale. His discoveries have led to the development of an entirely new method called quantum interferometry. This method has led to the development of a rich variety of instruments of extraordinary sensitivity and precision with application in wide areas of science and technology.

Esaki, Giaever and Josephson have through their discoveries opened up new fields of research in physics. They are closely related because the pioneering work by Esaki provided the foundation and direct impetus for Giaever’s discovery and Giaever’s work in turn provided the stimulus which led to Jo- sephson’s theoretical predictions. The close relation between the abstract concepts and sophisticated tools of modern physics and the practical applications to science and technology is strongly emphasized in these discoveries. The applications of solid state tunnelling already cover a wide range. Many devices based on tunneling are now used in electronics. The new quantum interferometry has already been used in such different applications as measurements of temperatures near the absolute zero, to detect gravitational waves, for ore prospecting, for communication through water and through mountains, to study the electromagnetic field around the heart or brain, to mention a few examples.

Drs. Esaki, Giaever and Josephson,

In a series of brilliant experiments and calculations you have explored different aspects of tunelling phenomena in solids. Your discoveries have opened up new fields of research and have given new fundamental insight about electrons in semiconductors and superconductors and about macroscopic quantum phenomena in superconductors.

On behalf of the Royal Academy of Sciences I wish to express our admiration and convey to you our warmest congratulations. I now ask you to proceed to receive your prizes from the hands of his Majesty the King.

Presentation Speech by professor Stig Lundqvist, Chalmers University of Technology

Translation from the Swedish text

Your Royal Highnesses, Ladies and Gentlemen,

The 1972 Nobel Prize for physics has been awarded to Drs John Bardeen, Leon N. Cooper and J. Robert Schrieffer for their theory of superconductivity, usually referred to as the BCS-theory.

Superconductivity is a peculiar phenomenon occurring in many metallic materials. Metals in their normal state have a certain electrical resistance, the magnitude of which varies with temperature. When a metal is cooled its resistance is reduced. In many metallic materials it happens that the electrical resistance not only decreases but also suddenly disappears when a certain critical temperature is passed which is a characteristic property of the material.

This phenomenon was discovered as early as 1911 by the Dutch physicist Kamerlingh Onnes, who was awarded the Nobel Prize for Physics in 1913 for his discoveries.

The term superconductivity refers to the complete disappearance of the electrical resistance, which was later verified with an enormous accuracy. A lead ring carrying a current of several hundred ampères was kept cooled for a period of 2 1/2 years with no measurable change in the current.

An important discovery was made in the thirties, when it was shown that an external magnetic field cannot penetrate a superconductor. If you place a permanent magnet in a bowl of superconducting material, the magnet will hover in the air above the bowl, literally floating on a cushion of its own magnetic field lines. This effect may be used as an example for the construction of friction-free bearings.

Many of the properties of a metal change when it becomes superconducting and new effects appear which have no equivalent in the former’s normal state. Numerous experiments have clearly shown that a fundamentally new state of the metal is involved.

The transition to the superconductive state occurs at extremely low temperatures, characteristically only a few degrees above absolute zero. For this reason, practical applications of the phenomenon have been rare in the past and superconductivity has been widely considered as a scientifically interesting but exclusive curiosity confined to the low temperature physics laboratories. This state of affairs is rapidly changing and the use of superconducting devices is rapidly increasing. Superconducting magnets are often used for example in particle accelerators. Superconductivity research has in recent years resulted in substantial advances in measuring techniques and an extensive used in the computer field is also highly probable. Advanced plans for the use of superconductivity in heavy engineering are also in existence. By way of an example, it may be mentioned that the transport of electric energy to the major cities of the world with the use of superconductive lines is being planned. Looking further ahead one can see, for example, the possibility of building ultrarapid trains that run on superconducting tracks.

Superconductivity has been studied experimentally for more than sixty years. However, the central problem, the question of the physical mechanism responsible for the phenomenon remained a mystery until the late fifties. Many famous physicists tackled the problem with little success. The difficulties were related to the very special nature of the mechanism sought. In a normal metal the electrons more around individually at random, somewhat similar to the atoms in a gas, and the theory is, in principle, fairly simple. In superconductive metals the experiments suggested the existence of a collective state of the conduction electrons-a state in which the electrons are strongly coupled and their motion correlated so that there is a gigantic coherent state of macroscopic dimension containing an enormous number of electrons. The physical mechanism responsible for such a coupling remained unknown for a long time. An important step towards the solution was taken in 1950 when it was discovered simultaneously on theoretical and experimental grounds that superconductivity must be connected with the coupling of the electrons to the vibrations of the atoms in the crystal lattice. The conduction electrons are coupled to each other via these vibrations. Starting from this fundamental coupling of the electrons Bardeen, Cooper and Schrieffer developed their theory of superconductivity, published in 1957, which gave a complete theoretical explanation of the phenomenon of superconductivity.

According to their theory, the coupling of the electrons to the lattice oscillations leads to the formation of bound pairs of electrons. These pairs play a fundamental role in the theory. The complete picture of the mechanism of superconductivity appeared when Bardeen, Cooper, and Schrieffer showed that the motion of the different pairs is very strongly correlated and that this leads to the formation of a gigantic coherent state in which a large number of electrons participate. It is this ordered motion of the electrons in the superconductive state in contrast to the random individual motion in a normal crystal that gives superconductivity its special properties.

The theory developed by Bardeen, Cooper, and Schrieffer together with extensions and refinements of the theory, which followed in the years after 1957, succeeded in explaining in considerable detail the properties of superconductors. The theory also predicted new effects and it stimulated intense activity in theoretical and experimental research which opened up new areas. These latter developments have led to new important discoveries which are being used in a number of interesting ways especially in the sphere of measuring techniques.

Developments in the field of superconductivity during the last fifteen years have been greatly inspired by the fundamental theory of superconductivity and have strikingly verified the validity and great range of the concepts and ideas developed by Bardeen, Cooper, and Schrieffer.

Drs. Bardeen, Cooper, and Schrieffer,

You have in your fundamental work given a complete theoretical explanation of the phenomenon of superconductivity. Your theory has also predicted new effects and stimulated an intensive activity in theoretical and experimental research. The further developments in the field of superconductivity have in a striking way confirmed the great range and validity of the concepts and ideas in your fundamental paper from 1957.

On behalf of the Royal Academy of Sciences, I wish to convey to you the warmest congratulations and I now ask you to receive your prizes from the Hands of His Royal Highness the Crown Prince.

Presentation Speech by professor Stig Lundqvist, Chalmers University of Technology

Translation from the Swedish text

Your Royal Highnesses, Ladies and Gentlemen,

The 1972 Nobel Prize for physics has been awarded to Drs John Bardeen, Leon N. Cooper and J. Robert Schrieffer for their theory of superconductivity, usually referred to as the BCS-theory.

Superconductivity is a peculiar phenomenon occurring in many metallic materials. Metals in their normal state have a certain electrical resistance, the magnitude of which varies with temperature. When a metal is cooled its resistance is reduced. In many metallic materials it happens that the electrical resistance not only decreases but also suddenly disappears when a certain critical temperature is passed which is a characteristic property of the material.

This phenomenon was discovered as early as 1911 by the Dutch physicist Kamerlingh Onnes, who was awarded the Nobel Prize for Physics in 1913 for his discoveries.

The term superconductivity refers to the complete disappearance of the electrical resistance, which was later verified with an enormous accuracy. A lead ring carrying a current of several hundred ampères was kept cooled for a period of 2 1/2 years with no measurable change in the current.

An important discovery was made in the thirties, when it was shown that an external magnetic field cannot penetrate a superconductor. If you place a permanent magnet in a bowl of superconducting material, the magnet will hover in the air above the bowl, literally floating on a cushion of its own magnetic field lines. This effect may be used as an example for the construction of friction-free bearings.

Many of the properties of a metal change when it becomes superconducting and new effects appear which have no equivalent in the former’s normal state. Numerous experiments have clearly shown that a fundamentally new state of the metal is involved.

The transition to the superconductive state occurs at extremely low temperatures, characteristically only a few degrees above absolute zero. For this reason, practical applications of the phenomenon have been rare in the past and superconductivity has been widely considered as a scientifically interesting but exclusive curiosity confined to the low temperature physics laboratories. This state of affairs is rapidly changing and the use of superconducting devices is rapidly increasing. Superconducting magnets are often used for example in particle accelerators. Superconductivity research has in recent years resulted in substantial advances in measuring techniques and an extensive used in the computer field is also highly probable. Advanced plans for the use of superconductivity in heavy engineering are also in existence. By way of an example, it may be mentioned that the transport of electric energy to the major cities of the world with the use of superconductive lines is being planned. Looking further ahead one can see, for example, the possibility of building ultrarapid trains that run on superconducting tracks.

Superconductivity has been studied experimentally for more than sixty years. However, the central problem, the question of the physical mechanism responsible for the phenomenon remained a mystery until the late fifties. Many famous physicists tackled the problem with little success. The difficulties were related to the very special nature of the mechanism sought. In a normal metal the electrons more around individually at random, somewhat similar to the atoms in a gas, and the theory is, in principle, fairly simple. In superconductive metals the experiments suggested the existence of a collective state of the conduction electrons-a state in which the electrons are strongly coupled and their motion correlated so that there is a gigantic coherent state of macroscopic dimension containing an enormous number of electrons. The physical mechanism responsible for such a coupling remained unknown for a long time. An important step towards the solution was taken in 1950 when it was discovered simultaneously on theoretical and experimental grounds that superconductivity must be connected with the coupling of the electrons to the vibrations of the atoms in the crystal lattice. The conduction electrons are coupled to each other via these vibrations. Starting from this fundamental coupling of the electrons Bardeen, Cooper and Schrieffer developed their theory of superconductivity, published in 1957, which gave a complete theoretical explanation of the phenomenon of superconductivity.

According to their theory, the coupling of the electrons to the lattice oscillations leads to the formation of bound pairs of electrons. These pairs play a fundamental role in the theory. The complete picture of the mechanism of superconductivity appeared when Bardeen, Cooper, and Schrieffer showed that the motion of the different pairs is very strongly correlated and that this leads to the formation of a gigantic coherent state in which a large number of electrons participate. It is this ordered motion of the electrons in the superconductive state in contrast to the random individual motion in a normal crystal that gives superconductivity its special properties.

The theory developed by Bardeen, Cooper, and Schrieffer together with extensions and refinements of the theory, which followed in the years after 1957, succeeded in explaining in considerable detail the properties of superconductors. The theory also predicted new effects and it stimulated intense activity in theoretical and experimental research which opened up new areas. These latter developments have led to new important discoveries which are being used in a number of interesting ways especially in the sphere of measuring techniques.

Developments in the field of superconductivity during the last fifteen years have been greatly inspired by the fundamental theory of superconductivity and have strikingly verified the validity and great range of the concepts and ideas developed by Bardeen, Cooper, and Schrieffer.

Drs. Bardeen, Cooper, and Schrieffer,

You have in your fundamental work given a complete theoretical explanation of the phenomenon of superconductivity. Your theory has also predicted new effects and stimulated an intensive activity in theoretical and experimental research. The further developments in the field of superconductivity have in a striking way confirmed the great range and validity of the concepts and ideas in your fundamental paper from 1957.

On behalf of the Royal Academy of Sciences, I wish to convey to you the warmest congratulations and I now ask you to receive your prizes from the Hands of His Royal Highness the Crown Prince.

Presentation Speech by professor Stig Lundqvist, Chalmers University of Technology

Translation from the Swedish text

Your Royal Highnesses, Ladies and Gentlemen,

The 1972 Nobel Prize for physics has been awarded to Drs John Bardeen, Leon N. Cooper and J. Robert Schrieffer for their theory of superconductivity, usually referred to as the BCS-theory.

Superconductivity is a peculiar phenomenon occurring in many metallic materials. Metals in their normal state have a certain electrical resistance, the magnitude of which varies with temperature. When a metal is cooled its resistance is reduced. In many metallic materials it happens that the electrical resistance not only decreases but also suddenly disappears when a certain critical temperature is passed which is a characteristic property of the material.

This phenomenon was discovered as early as 1911 by the Dutch physicist Kamerlingh Onnes, who was awarded the Nobel Prize for Physics in 1913 for his discoveries.

The term superconductivity refers to the complete disappearance of the electrical resistance, which was later verified with an enormous accuracy. A lead ring carrying a current of several hundred ampères was kept cooled for a period of 2 1/2 years with no measurable change in the current.

An important discovery was made in the thirties, when it was shown that an external magnetic field cannot penetrate a superconductor. If you place a permanent magnet in a bowl of superconducting material, the magnet will hover in the air above the bowl, literally floating on a cushion of its own magnetic field lines. This effect may be used as an example for the construction of friction-free bearings.

Many of the properties of a metal change when it becomes superconducting and new effects appear which have no equivalent in the former’s normal state. Numerous experiments have clearly shown that a fundamentally new state of the metal is involved.

The transition to the superconductive state occurs at extremely low temperatures, characteristically only a few degrees above absolute zero. For this reason, practical applications of the phenomenon have been rare in the past and superconductivity has been widely considered as a scientifically interesting but exclusive curiosity confined to the low temperature physics laboratories. This state of affairs is rapidly changing and the use of superconducting devices is rapidly increasing. Superconducting magnets are often used for example in particle accelerators. Superconductivity research has in recent years resulted in substantial advances in measuring techniques and an extensive used in the computer field is also highly probable. Advanced plans for the use of superconductivity in heavy engineering are also in existence. By way of an example, it may be mentioned that the transport of electric energy to the major cities of the world with the use of superconductive lines is being planned. Looking further ahead one can see, for example, the possibility of building ultrarapid trains that run on superconducting tracks.

Superconductivity has been studied experimentally for more than sixty years. However, the central problem, the question of the physical mechanism responsible for the phenomenon remained a mystery until the late fifties. Many famous physicists tackled the problem with little success. The difficulties were related to the very special nature of the mechanism sought. In a normal metal the electrons more around individually at random, somewhat similar to the atoms in a gas, and the theory is, in principle, fairly simple. In superconductive metals the experiments suggested the existence of a collective state of the conduction electrons-a state in which the electrons are strongly coupled and their motion correlated so that there is a gigantic coherent state of macroscopic dimension containing an enormous number of electrons. The physical mechanism responsible for such a coupling remained unknown for a long time. An important step towards the solution was taken in 1950 when it was discovered simultaneously on theoretical and experimental grounds that superconductivity must be connected with the coupling of the electrons to the vibrations of the atoms in the crystal lattice. The conduction electrons are coupled to each other via these vibrations. Starting from this fundamental coupling of the electrons Bardeen, Cooper and Schrieffer developed their theory of superconductivity, published in 1957, which gave a complete theoretical explanation of the phenomenon of superconductivity.

According to their theory, the coupling of the electrons to the lattice oscillations leads to the formation of bound pairs of electrons. These pairs play a fundamental role in the theory. The complete picture of the mechanism of superconductivity appeared when Bardeen, Cooper, and Schrieffer showed that the motion of the different pairs is very strongly correlated and that this leads to the formation of a gigantic coherent state in which a large number of electrons participate. It is this ordered motion of the electrons in the superconductive state in contrast to the random individual motion in a normal crystal that gives superconductivity its special properties.

The theory developed by Bardeen, Cooper, and Schrieffer together with extensions and refinements of the theory, which followed in the years after 1957, succeeded in explaining in considerable detail the properties of superconductors. The theory also predicted new effects and it stimulated intense activity in theoretical and experimental research which opened up new areas. These latter developments have led to new important discoveries which are being used in a number of interesting ways especially in the sphere of measuring techniques.

Developments in the field of superconductivity during the last fifteen years have been greatly inspired by the fundamental theory of superconductivity and have strikingly verified the validity and great range of the concepts and ideas developed by Bardeen, Cooper, and Schrieffer.

Drs. Bardeen, Cooper, and Schrieffer,

You have in your fundamental work given a complete theoretical explanation of the phenomenon of superconductivity. Your theory has also predicted new effects and stimulated an intensive activity in theoretical and experimental research. The further developments in the field of superconductivity have in a striking way confirmed the great range and validity of the concepts and ideas in your fundamental paper from 1957.

On behalf of the Royal Academy of Sciences, I wish to convey to you the warmest congratulations and I now ask you to receive your prizes from the Hands of His Royal Highness the Crown Prince.

Presentation Speech by Professor I. Waller, member of the Swedish Academy of Sciences

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen.

The winner of this year’s Nobel Prize in Physics, Professor Lev Davidovic Landau at Moscow University, was born in Baku, 1908. His mathematical talents appeared at a very early age and at the age of 14 he began his studies at the University of Leningrad. After finishing them he spent one and a half years abroad, in particular with the well-known atomic physicist Niels Bohr in Copenhagen. He made a strong impression during this time thanks to his brilliant intellect and great outspokenness.

In 1930 Landau published a quantum theoretical investigation concerning the behaviour of free electrons in a magnetic field which immediately gave him international fame. This work turned out to be essential for the understanding of the properties of metals. Starting from new fruitful ideas Landau found after his return home, often in collaboration with his pupils, important results concerning the structure of magnetic substances and supraconductors and advanced fundamental theories for phase transformations and thermodynamical fluctuations.

Landau’s ability to see the core of a problem and his unique physical intuition appear clearly in his investigations on liquid helium which he started after having been attached in 1937 to the Institute for Physical Problems in Moscow. The head of this institute was the famous physicist Kapitsa who then performed interesting experiments on liquid helium. The natural helium gas had earlier been liquefied by cooling to about four degrees above the absolute zero of temperature and subsequent research had shown that this fluid when further cooled about two degrees was transformed to a new state which has quite strange properties. According to a term introduced by Kapitsa it is superfluid which means that it can easily flow through very fine capillaries and slits which almost completely prevent the flow of all other liquids.

The originality in Landau’s attack on the problem of explaining these phenomena was that he considered the quantized states of motion of the whole liquid instead of the states of the single atoms as other scientists had done earlier. Landau started by considering the state of the fluid at the absolute zero temperature which is its ground state. He described the excited states of the liquid by the motion of certain fictive particles called quasiparticles. Landau combined experimental results with his calculations and deduced in this way the mechanical properties of the quasi-particles. These results, from which the properties of the fluid could be calculated, were later directly confirmed by investigations on the scattering of neutrons in liquid helium. Such experiments were first performed at Atomic Energy Ltd. in Stockholm in 1957. Landau further found that there exists in liquid helium besides ordinary sound waves also waves of a “second sound”. He inspired thereby a Russian scientist to confirm this phenomenon experimentally.

Natural helium consists of an isotope of atomic weight 4 apart from about one millionth of another isotope of atomic weight 3. The lighter isotope has been studied in the liquid state since about 1950. This kind of liquid helium has properties which are quite different from those of the heavier isotope because the helium nuclei of atomic weights 3 and 4 are essentially different. A satisfactory theory for the lighter helium liquid was first given by Landau in 1956 – 1958 and has many formal similarities with his above-mentioned theory for the heavier isotope. The new theory is valid only at very low temperatures, less than one tenth of a degree above absolute zero. This is, however, the most interesting temperature range. Due to the difficulty of making measurements at these low temperatures the theory was not experimentally tested until very recently. These tests have been the more favourable for the theory the more the measuring technique has been refined. Landau has also predicted a new kind of wave propagation for this liquid and has called it zero sound. He has thereby stimulated experimental scientists to great efforts aiming to detect zero sound.

The importance of Landau’s investigations are apparent when one considers that an important goal of physics research is to explain the properties of liquids as completely as it has been possible to explain the properties of crystals and of rarefied gases. In their efforts to attain this goal the scientists have in general met with insurmountable difficulties. An essential exception is Landau’s theories of liquid helium which therefore are an achievement of great and profound importance.

Besides his investigations on condensed matter, i.e. matter in the solid and liquid state for which he is now awarded the Nobel Prize, Landau has also made contributions of the utmost importance to other parts of physics, in particular to the theories of quantized fields and of elementary particles. He has by his original ideas and masterly investigations exercised far-reaching influence on the evolution of the atomic science of our time.

Professor Landau has unfortunately not yet fully recovered from the severe accident which he sustained at the beginning of this year. He is therefore not here to receive his Nobel Prize which is instead handed to him today by the Ambassador of Sweden in Moscow. On behalf of the Swedish Academy of Sciences I wish to express the hope that Professor Landau will soon completely recover.

Presentation Speech by former Councillor Th. Nordstrom, President of the Royal Swedish Academy of Sciences, on December 10, 1913

Your Majesty, Your Royal Highnesses, Ladies and Gentlemen.

At its meeting on the 11th November the Royal Academy of Sciences decided to award the Nobel Prize for Physics for the year 1913 to Dr. Heike Kamerlingh Onnes, Professor at the University of Leyden “for his investigations on the properties of matter at low temperatures which led, inter alia, to the production of liquid helium”.

As early as 100 years ago research into the behaviour of gases at various pressures and temperatures gave a great impetus to physics. Since this time the study of the connection between the pressure, the volume and the temperature of gases has played a very important part in physics, and particularly in thermodynamics – one of the most important disciplines of modern physics.

In the years 1873 and 1880 Van der Waals presented his famous laws governing gases which, owing to their great importance for thermodynamics, were rewarded by the Royal Academy of Sciences in 1910 with the Nobel Prize for Physics.

The thermodynamic laws of Van der Waals were laid down on atheoretical basis under the assumption that certain properties could be attributed to molecules and molecular forces. In the case of gases the properties of which are changed by pressure and temperature, or in one way or another do not agree with Van der Waals’ hypothesis, deviations from these laws occur.

A systematic experimental study of these deviations and the changes they undergo due to temperature and the molecular structure of the gas must therefore contribute greatly to our knowledge of the properties of the molecules and of the phenomena associated with them.

It was for this research that Kamerlingh Onnes set up his famous laboratory at the beginning of the 1880’s, and in it he designed and improved, with unusual success, the physical apparatus needed for his experiments.

It is impossible to report briefly here on the many important results of this work. They embrace the thermodynamic properties at low temperatures of a series of monatomic and diatomic gases and their mixtures, and have contributed to the development of modern thermodynamics and to an elucidation of those associated phenomena which are so difficult to explain. They have also made very important contributions to our knowledge of the structure of matter and of phenomena related to it.

Whilst important on its own account, this research has gained greater significance because it has led to the attainment of the lowest temperatures so far reached. These lie in the vicinity of so-called absolute zero, the lowest temperature in thermodynamics.

The attainment of low temperatures in general was not possible until we learnt to condense the so-called permanent gases, which, since Faraday’s pioneer work in this field in the middle of the 1820’s, has been one of the most important tasks of thermodynamics.

After Olszewski, Linde, and Hampson had prepared liquid oxygen and air in a variety of ways, and after Dewar, having overcome great experimental difficulties, had succeeded in condensing hydrogen, all temperatures down to -259°C, i.e. all temperatures down to 14° from absolute zero, could be attained.

At these low temperatures all known gases can easily be condensed, except for helium, which was discovered in the atmosphere in the year 1895.

Thus, by condensing this it would be possible to reach still lower temperatures. After both Olszewski and Dewar, Travers, and Jacquerod had tried in vain to prepare liquid helium, using a variety of met hods it was generally assumed that it was impossible.

The question was solved in 1908, however, by Kamerlingh Onnes, who then prepared liquid helium for the first time.

I should have to cover too much ground if I were to report here on the experimental equipment with which Kamerlingh Onnes was at last successful in liquefying helium, and on the enormous experimental difficulties which had to be overcome. I would only mention here that the liquefaction of helium represented a continuation of the long series of investigations into the properties of gases and liquids at low temperatures which Kamerlingh Onnes has carried out in so praiseworthy a manner. These investigations finally led to the determination of the so-called isotherms of helium and the knowledge gained here was the first step towards the liquefaction of helium. Kamerlingh Onnes has constructed cold baths with liquid helium which permit research to be done into the properties of substances at temperatures which lie between 4,3° and 1,15° from absolute zero.

The attainment of these low temperatures is of the greatest importance to physics research, for at these temperatures both the properties of the substances and also the course followed by physical phenomena, are generally quite different from those at our normal and higher temperatures, and a knowledge of these changes is of fundamental importance in answering many of the questions of modern physics.

Let me mention one of these particularly here.

Various principles borrowed from gas thermodynamics have been transferred to the so-called theory of electrons, which is the guiding principle in physics in explaining all electrical, magnetic, optical, and many heat phenomena.

The laws which have been arrived at in this way also seem to be confirmed by measurements at our normal and higher temperatures. That the situation is at very low temperatures not the same, however, has, amongst other things, been shown by Kamerlingh Onnes’ experiments on resistance to electrical conduction at helium temperatures and by the determinations which Nernst and his students have carried out in relation to specific heat at liquid temperatures.

It has become more and more clear that a change in the whole theory of electrons is necessary. Theoretical work in this direction has already been begun by a number of research workers, particularly by Planck and Einstein.

In the meantime, new supports had to be created for these investigations. These could only be obtained by a continued experimental study of the properties of substances at low temperatures, particularly at helium temperatures, which are the most suitable for throwing light upon phenomena in the world of electrons. Kamerlingh Onnes’ merit lies in the fact that he has created these possibilities and at the same time opened up a field of the greatest consequence and significance to physical science.

Owing to the great importance which Kamerlingh Onnes’ work has been seen to have for research in physics, the Royal Academy of Sciences has found ample grounds for bestowing upon him the Nobel Prize for Physics for the year 1913.