Vacancy spectroscopy of non-Abelian Kitaev spin liquids

TL;DR

This paper predicts spectroscopic signatures of Majorana zero modes in non-Abelian Kitaev spin liquids with vacancies, proposing observable features in tunneling conductance that can be tested in current experiments on $
$-RuCl$_3$.

Contribution

It introduces a novel spectroscopic signature, a quasi-zero-voltage peak, linked to Majorana zero modes in vacancy-rich Kitaev spin liquids, guiding experimental detection.

Findings

Identification of a quasi-zero-voltage peak in tunneling conductance.

Detection of a Van Hove singularity indicating Majorana fermion energy scale.

Relevance of results to current $
$-RuCl$_3$ experiments.

Abstract

Spin vacancies in the non-Abelian Kitaev spin liquid are known to harbor Majorana zero modes, potentially enabling topological quantum computing at elevated temperatures. Here, we study the spectroscopic signatures of such Majorana zero modes in a scanning tunneling setup where a non-Abelian Kitaev spin liquid with a finite density of spin vacancies forms a tunneling barrier between a tip and a substrate. Our key result is a well-defined peak close to zero bias voltage in the derivative of the tunneling conductance whose voltage and intensity both increase with the density of vacancies. This ''quasi-zero-voltage peak'' is identified as the closest analog of the zero-voltage peak observed in topological superconductors that additionally reflects the fractionalized nature of spin-liquid-based Majorana zero modes. We further highlight a single-fermion Van Hove singularity at a higher voltage that reveals the energy scale of the emergent Majorana fermions in the Kitaev spin liquid. Our proposed signatures are within reach of current experiments on the candidate material $\alpha$-RuCl$_3$.