Photon-Assisted Seebeck Effect in a Quantum Dot Coupled to Majorana Zero Modes

Tian-Yu He,Hailing Sun,Guofu Zhou

doi:10.3389/fphy.2021.687438

Abstract

The Seebeck effect is investigated within the framework of a non-equilibrium Green's function technique in a quantum dot (QD) sandwiched between the left and right leads held at different temperatures. We consider that the QD is shelled by a photon field and is side-coupled to a topological superconductor nanowire hosting Majorana zero modes (MZMs). It is found that the thermopower (Seebeck coefficient) can be obviously enhanced by weak QD-MZMs coupling at low temperatures, in addition to its sign reversion that may be used for detecting the existence of MZMs. In the presence of a photon field, the thermopower can be further enhanced due to decreased electrical conductance when electrons' transport probability through each channel is reduced by photon-assisted tunneling (PAT). The hybridization between the MZMs will also induce sign reversion of the thermopower in the absence of a photon field, whereas it has less impact on the thermopower when the QD is shelled by the photon field.

Highlights

Majorana zero modes (MZMs) [1, 2] are zero-energy excitations that have been extensively studied in the condensed matter physics community for much of the last decade
We study the Seebeck effect in a hybridized quantum dot (QD)-topological superconductor nanowire with a photon field shelled on the QD
When the two modes of the MZMs are strongly overlapped with each other, the thermopower is less influenced by the MZMs in the presence of the photon field because the photon energy absorbed by one mode of the MZMs is subsequently emitted by the other one

Summary

INTRODUCTION

Majorana zero modes (MZMs) [1, 2] are zero-energy excitations that have been extensively studied in the condensed matter physics community for much of the last decade. In 2008, Fu and Kane proved the theory that it is possible to induce MZMs in vortices by the means of the proximity effect between an s-wave superconductor and the surface states of a strong topological insulator It was subsequently demonstrated in experiments and has led to numerous studies [9, 10]. We study the Seebeck effect in a hybridized QD-topological superconductor nanowire with a FIGURE 1 | Schematic plot of the scheme composing a quantum dot connected to the left and right leads at different temperatures of TL and TR, respectively. We calculate the electrical conductance and thermopower through the dot interacting with one mode of the MZMs prepared at the ends of the topological superconductor nanowire. The dependence of thermopower on the dotMZMs coupling λ can be derived by Sommerfeld expansion of the Fermi function f (ε) up to second order in temperature, and its analytical expression when the dot level is near the chemical potential is [31, 34]

RESULTS AND DISCUSSION

CONCLUSIONS

DATA AVAILABILITY STATEMENT