CSC Logo & Symbolism
The CSC Logo depicts phenomena associated with three Nobel Prizes in Superconductivity and with the Meissner Effect.
- The red arrow on the right represents the persistent electric current resulting from the zero resistance of a superconductor. Heike Kamerlingh Onnes received the Nobel Prize in Physics in 1913 for his studies at liquid helium temperatures which included the discovery of superconductivity.
- The four golden horizontal lines symbolize the exclusion of magnetic field lines from the interior of a superconductor. This is known as the Meissner Effect, which was discovered by Fritz Meissner and Robert Ochsenfeld in 1933. It is associated with a perfectly diamagnetic state in a Type I superconductor, and is evidence that superconductivity is a thermodynamic phase independent of the path chosen to reach it.
- The two opposing black arrows, one with a yellow dot and the other with a yellow "x" at the center represent electrons with opposite spins but with equal and opposite momenta. These "paired electrons" are known as Cooper pairs. The many body properties of these Cooper pairs led to the development of a microscopic theory of superconductivity by John Bardeen, Leon Cooper and J. Robert Schrieffer, who received the Nobel Prize in Physics in 1972 for their theory, which is commonly known as the "BCS Theory."
- The green "X" on the left of the diagram is the symbol for a Josephson tunneling junction in electric circuits. Brian David Josephson received the Nobel Prize in Physics for his theoretical prediction that, under certain conditions, a supercurrent could flow through a tunnel barrier when no voltage is applied.
The logo is relevant to other superconducting effects that are not directly illustrated in the Logo. The simplest connection is to single quasi-particle tunneling into a superconductor, discovered by Ivar Giaever (Nobel Prize 1973). If sufficient current is passed through a Josephson junction or a superconducting tunnel junction, a voltage will appear across the tunnel junction and the current vs. voltage curve can be used to measure the superconducting energy gap.
High temperature ceramic oxide superconductors were synthesized in 1986 by J. Georg Bednorz and K. Alexander Müller (Nobel Prize 1987). Superconductivity was confirmed in these oxides when the effects described in the CSC Logo, specifically zero resistance, the Meissner Effect and tunneling of both paired and single quasi particles, were established.
Magnetization curves similar to those found for Type II superconductors, whose magnetization curves are fully diamagnetic up to a lower critical field, Hc1, whereupon magnetic field lines penetrate the superconductor up to an upper critical field, Hc2, where superconductivity disappears, (see 2003 Nobel Prize), but which were irreversible had been obtained for superconducting materials that were inhomogeneous, and therefore, were assumed not to be thermodynamic phases. It was not until Alexei A. Abrikosov developed his theory for Type II superconductors, that the possibility was recognized that these would display reversible magnetization curves that were not fully diamagnetic. Once the reversible character of their magnetization curves was established, Type II superconductors satisfied the principal conditions implied by the CSC Logo. Namely, superconductivity is a reversible thermodynamic phase whose properties do not depend on the path taken to achieve the superconducting state.