Quantum impurity spin in Majorana edge fermions

TL;DR

This paper investigates the interaction between impurity spins and Majorana edge modes in topological superconductors, revealing Ising-like behavior and mapping to the anisotropic Kondo model, with implications for probing order parameters.

Contribution

It demonstrates that Majorana edge modes exhibit Ising-like spin density and establishes a connection to the anisotropic Kondo model under magnetic fields.

Findings

Impurity spins couple to Majorana modes via Ising interactions.

External magnetic fields allow mapping to the anisotropic Kondo model.

Impurity magnetic response can probe the superconductor's order parameter.

Abstract

We show that Majorana edge modes of two-dimensional spin-triplet topological superconductors have Ising-like spin density whose direction is determined by the d-vector characterizing the spin-triplet pairing symmetry. Exchange coupling between an impurity spin (S=1/2) and Majorana edge modes is thus Ising-type. Under external magnetic field perpendicular to the Ising axis, the system can be mapped to a two-level system with Ohmic dissipation, which is equivalent to the anisotropic Kondo model. The magnetic response of the impurity spin can serve as a local experimental probe for the order parameter.