Magnetic impurities on the surface of topological superconductor

TL;DR

This paper investigates how magnetic impurities affect the surface states of a topological superconductor, revealing localized bound states, spin textures, and magnetic ordering driven by Majorana fermions.

Contribution

It demonstrates the formation of in-gap bound states, analyzes impurity spin-textures, and shows that RKKY interactions lead to magnetic order on the superconductor surface.

Findings

Single magnetic impurities induce in-gap bound states.

Impurity spin-texture is highly sensitive to impurity orientation.

Magnetic impurities can develop long-range order, breaking time-reversal symmetry.

Abstract

We consider the effects of magnetic impurities on the surface of superconducting Cu doped $Bi_{2}Se_{3}$ in the odd parity pairing phase which support topologically protected Majorana fermions surface states with linear spectrum. We show that a single magnetic impurity on the surface may induce a pair of in-gap localized bound states. The energy of the in-gap state is extremely sensitive to the orientation of the magnetic impurity due to the so-called Ising properties of Majorana fermions. The magnetic impurity induced spin-texture, which can be measured using spin sensitive STM, is calculated. We also show that the RKKY interactions between magnetic impurities mediated via the Majorana fermions are always ferromagnetic and dense enough magnetic impurities will develop long-range magnetic order and break the time-reversal symmetry on the material surface eventually.