Transport in a hybrid normal-topological superconductor Kondo model

TL;DR

This paper studies how Majorana bound states influence electron transport in a Kondo quantum dot system, revealing new energy scales and distinctive conductance behaviors that could help detect Majorana modes.

Contribution

It introduces the impact of Majorana modes on Kondo physics, identifying a new energy scale and analyzing transport properties under equilibrium and non-equilibrium conditions.

Findings

Emergence of a new energy scale T* < T_K affecting low-energy physics

Suppressed ac-conductance below T* at low temperatures

Negative differential conductance in non-equilibrium conditions

Abstract

We investigate the equilibrium and non-equilibrium transport through a quantum dot in the Kondo regime, embedded between a normal metal and a topological superconductor supporting Majorana bound states at its end points. We find that the Kondo physics is significantly modified by the presence of the Majorana modes. When the Majorana modes are coupled, aside from the Kondo scale $T_K$, a new energy scale $T^*\ll T_K$ emerges, that controls the low energy physics of the system. At low temperatures, the ac-conductance is suppressed for frequencies below $T^*$, while the noise spectrum acquires a $\sim \omega^3$ dependence. At high temperatures, $T \gg T_K$, the regular logarithmic dependence in the differential conductance is also affected. Under non-equilibrium conditions, and in particular in the $\{T, B\}\to 0$ limit, the differential conductance becomes negative. These findings indicate that the changes in transport may serve as clues for detecting the Majorana bound states in such systems. In terms of methods used, we characterize the transport by using a combination of perturbative and renormalization group approaches.