Obstructed insulators and flat bands in topological phase-change materials

TL;DR

This paper introduces the concept of amorphous obstructed insulators in topological phase-change materials, revealing their unique surface states and flat bands, which can be externally controlled, advancing understanding of their electronic properties.

Contribution

It defines a new electronic phase called amorphous obstructed insulator and demonstrates the presence of surface flat bands in 3D models, linking topological and obstructed properties.

Findings

Amorphous obstructed insulators host localized surface states.

3D models exhibit detectable surface flat bands via ARPES.

Topological properties can be switched externally in these materials.

Abstract

Phase-change materials are ubiquitous in technology because of their ability to transition between amorphous and crystalline phases fast and reversibly, upon shining light or passing a current. Here we argue that to fully understand their electronic properties it is necessary to define a novel electronic phase: the amorphous obstructed insulator. It differs from an obstructed insulator crystal in that it presents localized edge or surface states irrespective of the sample termination. Consequently, we show that obstructed amorphous insulators in three-dimensions host a surface two-dimensional flat band, detectable using ARPES. Our work establishes basic models for materials where topological and obstructed properties can be switched on and off externally, including two-dimensional surface flatbands.