Class D spectral peak in Majorana quantum wires

TL;DR

This paper investigates how disorder in Majorana quantum wires leads to a second spectral peak at the band center, which complicates the detection of Majorana states through spectroscopic methods.

Contribution

It reveals the emergence of a disorder-induced bandcenter anomaly that mimics Majorana signatures, highlighting challenges in experimental identification.

Findings

Disorder causes a narrow spectral peak at the band center.

The peak's properties are similar to Majorana states but originate differently.

The coexistence of Majorana and impurity peaks depends on quasiparticle state parity.

Abstract

Proximity coupled spin-orbit quantum wires have recently been shown to support midgap Majorana states at critical points. We show that in the presence of disorder these systems are prone to the buildup of a second bandcenter anomaly, which is of different physical origin but shares key characteristics with the Majorana state: it is narrow in width, insensitive to magnetic fields, carries unit spectral weight, and is rigidly tied to the band center. Depending on the parity of the number of subgap quasiparticle states, a Majorana mode does or does not coexist with the impurity generated peak. The strong 'entanglement' between the two phenomena may hinder an unambiguous detection of the Majorana by spectroscopic techniques.