Positron surface state as a spectroscopic probe for characterizing surfaces of topological insulator materials

TL;DR

This paper introduces positron annihilation spectroscopy as a novel, sensitive method for probing and characterizing topological surface states in topological insulators, supported by experimental and theoretical evidence.

Contribution

It demonstrates the existence of a positron surface state on Bi$_2$Te$_2$Se and shows the potential to detect topological surface states and their spin-texture using positron beams.

Findings

Existence of a positron surface state with binding energy 2.7 eV on Bi$_2$Te$_2$Se

Simulations predict detectable signals from topological surface states

Feasibility of using spin-polarized positrons to probe spin-texture

Abstract

Topological insulators are attracting considerable interest due to their potential for technological applications and as platforms for exploring wide-ranging fundamental science questions. In order to exploit, fine-tune, control and manipulate the topological surface states, spectroscopic tools which can effectively probe their properties are of key importance. Here, we demonstrate that positrons provide a sensitive probe for topological states, and that the associated annihilation spectrum provides a new technique for characterizing these states. Firm experimental evidence for the existence of a positron surface state near Bi$_2$Te$_2$Se with a binding energy of $E_b = 2.7 \pm 0.2 \, \text{eV}$ is presented, and is confirmed by first-principles calculations. Additionally, the simulations predict a significant signal originating from annihilation with the topological surface states and shows the feasibility to detect their spin-texture through the use of spin-polarized positron beams.