Josephson Effect in Quasi One-dimensional Unconventional Superconductors

Josephson effect in junctions of quasi one-dimensional superconductors at the quarter-filling electron density is discussed by using the tight-binding model on a two-dimensional square lattice. To consider the triangular lattice structures in real materials such as (TMTSF)₂X (X = PF₆, ClO₄, etc), the asymmetric hopping integral is introduced among second nearest lattice sites. A combination of these characters in superconductors (quasi one-dimensionality, quarter-filling electron density and weak triangular lattice structures) seriously affects the formation of a zero-energy state at a junction interface. As a consequence, calculated results of the Josephson current show anomalous dependences on temperatures.