Type II Superconductors: Experiments
The development of superconductors of the second kind has involved the usual strong interaction between experiment and theory. For superconductors of the second kind, the area enclosed by an ideal magnetization curve also equals the free energy difference between the state of perfect diamagnetism and the normal state. Goodman pointed out that the specific-heat jumps in a magnetic field observed in V3Ga could be understood in terms of the theory of type II superconductors. The three experiments giving most direct evidence for excitations in the vortex cores are observations of microwave absorption in a superconductor in the mixed state, specifìc-heat measurements in fields greater than Hc1(0), and studies of the nuclear magnetic resonance (NMR) relaxation rate. The author remarks that the two complementary features observed in the data for both intrinsic and alloy type II superconductors: First, the specific-heat jump and Second, the drastic change in slope of the magnetization curve at Hc2.