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Andreev bound states in Superconductor-quantum dot Josephson junction at infinite-U limit

Andreev bound states (ABSs) are studied in quantum dot coupled to conventional BCS superconducting leads on the basis of effective slave boson Hamiltonian in an infinite-U (Coulomb interaction) limit followed by Green's function technique. From the relevant Green's function, density of states (DOS) is analyzed at different superconducting phase differences. On the basis of numerical computation, it is pointed out from DOS plot that ABSs (sub-gap states) arise due to the phase difference between left and right superconducting leads. Due to the dependence on superconducting phase difference, ABSs are current carrying states. 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. These results are viewed in the light of existing theoretical analysis.