Robust spin-polarized midgap states at step edges of topological crystalline insulators

TL;DR

This study discovers robust, spin-polarized midgap states at step edges of topological crystalline insulators, which are stable against defects, magnetic fields, and temperature, promising for spintronics.

Contribution

It reveals the existence and stability of 1D midgap states at step edges of topological crystalline insulators, identified through spectroscopy and theoretical modeling.

Findings

Midgap states are spin-polarized flat bands connecting Dirac points.

States are robust against defects, magnetic fields, and high temperatures.

Experimental evidence confirms the topological protection of these states.

Abstract

Topological crystalline insulators are materials in which the crystalline symmetry leads to topologically protected surface states with a chiral spin texture, rendering them potential candidates for spintronics applications. Using scanning tunneling spectroscopy, we uncover the existence of one-dimensional (1D) midgap states at odd-atomic surface step edges of the three- dimensional topological crystalline insulator (Pb,Sn)Se. A minimal toy model and realistic tight- binding calculations identify them as spin-polarized flat bands connecting two Dirac points. This non-trivial origin provides the 1D midgap states with inherent stability and protects them from backscattering. We experimentally show that this stability results in a striking robustness to defects, strong magnetic fields, and elevated temperature.