Spin Seebeck effect induced by a Majorana zero mode in a nanomagnet

Abstract

Abstract In mesoscopic devices, spin-resolved thermoelectrics induced by Majorana zero modes (MZMs) has attracted much attention. In this work we study an exactly solvable model consisting of a quantum dot coupled to metallic leads and side-coupled to a local large spin and a topological superconductor wire hosting MZMs. Because of MZMs’ helical property, the spin-up component of the dot spin is coupled with the MZM We mainly focus on one of the thermoelectric quantities—the Seebeck coefficient. By using Green’s function method combined with Hubbard operators, we obtain an analytical result for the spectral function. Then it is shown that spin Seebeck effects are determined by the interplay of temperature, exchange coupling, and the strength of coupling to Majorana wire. It is found that the spin-up thermopower is immune to local impurities in the limit of low temperature or large coupling to topological superconductor. Then we show that the spin-resolved thermopowers exhibit angular-quantum-number-dependent zero points. Specifically, the spin-down thermopower exhibits 4 S + 1 zero points due to the presence of local large spin, and the spin-up thermopower exhibits 8 S + 3 zero points near the transition point (where the competition of hole and electron processes reaches equilibrium), due to the interplay of local large spin and MZM. The charge and spin Seebeck coefficients also show S -dependent and MZM-involved behaviors. The results show that the interplay of local large spin and Majorana zero mode generates some interesting results, which may provide additional information as the signature of Majorana zero modes.