Breakdown of Superconductivity in Small Metallic Grains
CHEN Zhi-Qian1,3, ZHENG Ren-Rong2,3
1Department of Physics, Southwest China Normal University, Chongqing 400715
2Department of Physics, Shanghai Teachers University, Shanghai 200234
3Department of Physics, Suzhou University, Suzhou 215006
Breakdown of Superconductivity in Small Metallic Grains
CHEN Zhi-Qian1,3;ZHENG Ren-Rong2,3
1Department of Physics, Southwest China Normal University, Chongqing 400715
2Department of Physics, Shanghai Teachers University, Shanghai 200234
3Department of Physics, Suzhou University, Suzhou 215006
Abstract： Superconductivity in small metallic grains is carefully checked as their size is decreased to a few nm when the average level spacing d could be compared with the bulk gap Δ. Using random matrix theory to the mean field, we find that the average theoretical values of the critical level spacing for both odd and even numbers of electrons and the transition temperature Tc in three Gauss ensembles are quite different for those from the model of uniformly spaced levels. For Sz = 1/2, as grain size is reduced, the transition temperature or the granular gap decreases monotonously, and the relation 2Δ ( 0 ) /кB Tc≤ 3.53 always exists.
2000, Vol. 17 
