Andreev Bound States in Superconductor-quantum Dot-superconductor Junction At Infinite-U Limit

Andreev bound states (ABSs) are studied in quantum dot coupled to conventional BCS superconducting leads at infinite-U (Coulomb inteaction) limit within the slave Boson mean field approximation employing Green's function approach. From the relevant Green's function, density of states (DOS) is analyzed at different superconducting phase differences and pointed out that ABSs (sub-gap states) arise due to the phase difference between left and right superconducting leads even at infinite-U limit. We have also analyzed the energy of ABSs as a function of phase difference between left and right superconducting lead for electron-hole symmetric as well as non-symmetric cases at various dot-lead coupling strengths. It is also pointed out that a finite internal gap arises between upper and lower Andreev bound states in the absence of electron-hole or left-right symmetry.