Excess photon-assisted noise of Majorana and Andreev bound states

TL;DR

This paper studies the excess photon-assisted noise in tunneling into Majorana and Andreev bound states, revealing distinct behaviors that can help identify topological superconducting states.

Contribution

It provides a theoretical analysis of excess photon-assisted noise under harmonic bias in Majorana and Andreev bound states, highlighting unique signatures for topological states.

Findings

Majorana states show multiple sign reversals in excess noise with increasing bias.

Andreev bound states exhibit strictly negative excess noise across bias range.

Distinct noise behaviors can serve as signatures for topological superconductivity.

Abstract

Photon-assisted tunneling arises under an ac bias, with the drive frequency setting the photon energy. The excess photon-assisted noise is defined as the difference between the shot noise under a combined dc and ac bias and that under a dc bias alone. We investigate this quantity in tunneling into Majorana or Andreev bound states, which are of great interest in the search for topological superconductors. Under a harmonic bias $V(t)=V_\mathrm{dc}[1-\cos(\Omega t)]$, the excess photon-assisted noise exhibits distinct behaviors: for Majorana or quasi-Majorana bound states, it undergoes multiple sign reversals as $V_\mathrm{dc}$ increases and vanishes at nonzero integer values of $eV_\mathrm{dc}/\Omega$ (with $e$ the elementary charge), whereas for zero-energy Andreev bound states--particularly those producing nearly quantized zero-bias conductance peaks--it remains strictly negative over the entire $V_\mathrm{dc}$ range.