Inelastic magnetic scattering effect on LDOS of topological insulators

TL;DR

This paper investigates how inelastic magnetic scattering from localized spins of magnetic ions affects the local density of states on topological insulator surfaces, revealing new low-energy anomalies that can be used for impurity spin spectroscopy.

Contribution

It introduces a theoretical framework for inelastic scattering effects on LDOS in topological insulators, considering magnetic anisotropies and bound state formation.

Findings

Inelastic scattering causes significant LDOS anomalies at low energies.

Magnetic anisotropies split impurity spin states, enabling inelastic processes.

Proposed spectroscopy method for impurity spins using LDOS tuning.

Abstract

Magnetic ions such as Fe, Mn and Co with localized spins may be adsorbed on the surface of topological insulators like \Bi. They form scattering centers for the helical surface states which have a Dirac cone dispersion as long as the local spins are disordered. However, the local density of states (LDOS) may be severely modified by the formation of bound states. Commonly only elastic scattering due to normal and exchange potentials of the adatom is assumed. Magnetization measurements show, however, that considerable magnetic single ion anisotropies exist which lead to a splitting of the local impurity spin states resulting in a singlet ground state. Therefore inelastic scattering processes of helical Dirac electrons become possible as described by a dynamical local self energy of second order in the exchange interaction. The self energy influences bound state formation and leads to significant new anomalies in the LDOS at low energies and low temperatures which we calculate within T-matrix approach. We propose that they may be used for spectroscopy of local impurity spin states by appropriate tuning of chemical potential and magnetic field.