Y. Shimizu et al., MULTILEVEL EFFECT ON THE JOSEPHSON CURRENT THROUGH A QUANTUM-DOT, Journal of the Physical Society of Japan, 67(5), 1998, pp. 1525-1528
Josephson current through a multilevel quantum dot with strong Coulomb
repulsion is studied by means of a Hartree-Fock approximation. We pay
attention to the offdiagonal Cooper pair tunneling process in which a
n up-spin electron and a down-spin electron are transferred to the opp
osite bank through different single-particle levels in the dot. It is
shown that; if the offdiagonal tunneling process is relevant, the syst
em can behave as a pi junction even when the dot is nonmagnetic withou
t a localized spin. It is also found that pi-junction behavior is enha
nced with increasing the number of the dot levels. On the other hand,
if the offdiagonal tunneling process is completely negligible, the mul
tilevel structure suppresses pi-junction behavior. These results indic
ate that we should take the multilevel effects into account in analyzi
ng the Josephson current through a correlated quantum dot.