Short Coherence Length Superconductors and the Fermi Velocity Paradox

Guy Deutscher；J. Bok

Chinese Journal of Physics

31卷6S期（1993 / 12 / 01）

805 - 812

英文

We compare the value for the coherence length calculated using the BCS theory with values of the Fermi velocity obtained either from band calculations or from Andreev reflection experiments, to experimental values. For low Tc superconductors the BCS values are in excellent quantitative agreement with experiment, but that for all known superconducting compounds having a critical temperature higher than 10 K, the experimental coherence length is anomalously short. We show that this may be explained by a wide spread in the Fermi velocity, with both high and low velocity carriers. This implies a density of states comprising a broad band and a narrow peak located at or near the Fermi level. The role of both kinds of carriers in achieving a high Tc is discussed.