Kondo effect in a quantum dot side-coupled to a topological superconductor

Abstract

We investigate the dynamical and transport features of a Kondo dot side coupled to a topological superconductor (TS). The Majorana fermion states (MFSs) formed at the ends of the TS are found to be able to alter the Kondo physics profoundly: For an infinitely long wire where the MFSs do not overlap (${\ensuremath{\epsilon}}_{m}=0$) a finite dot-MFS coupling $({\ensuremath{\Gamma}}_{m})$ reduces the unitary-limit value of the linear conductance by exactly a factor 3/4 in the weak-coupling regime $({\ensuremath{\Gamma}}_{m}l{T}_{K})$, where ${T}_{K}$ is the Kondo temperature. In the strong-coupling regime (${\ensuremath{\Gamma}}_{m}g{T}_{K})$, on the other hand, the spin-split Kondo resonance takes place due to the MFS-induced Zeeman splitting, which is a genuine many-body effect of the strong Coulomb interaction and the topological superconductivity. We find that the original Kondo resonance is fully restored once the MFSs are strongly hybridized (${\ensuremath{\epsilon}}_{m}g{\ensuremath{\Gamma}}_{m}$). This unusual interaction between the Kondo effect and the MFS can thus serve to detect the Majorana fermions unambiguously and quantify the degree of overlap between the MFSs in the TS.