Flat-lens focusing of electrons on the surface of a topological insulator

TL;DR

This paper proposes a flat-electronic lens on topological insulators that uses negative refraction from Fermi surface shape change to focus electrons, avoiding interband transitions and backscattering.

Contribution

It introduces a novel flat-electron lens design on topological insulators based on Fermi surface curvature change, expanding the scope of electron focusing techniques.

Findings

Negative refraction achieved without interband transitions.

Focusing effective over a broad range of incident angles.

Quantum interference pattern calculated for noncircular Fermi surfaces.

Abstract

We propose the implementation of an electronic Veselago lens on the conducting surface of a three-dimensional topological insulator (such as Bi2Te3). The negative refraction needed for such a flat lens results from the sign change of the curvature of the Fermi surface, changing from a circular to a snowflake-like shape across a sufficiently large electrostatic potential step. No interband transition (as in graphene) is needed. For this reason, and because the topological insulator provides protection against backscattering, the potential step is able to focus a broad range of incident angles. We calculate the quantum interference pattern produced by a point source, generalizing the analogous optical calculation to include the effect of a noncircular Fermi surface (having a nonzero conic constant).