ARPES in strongly disordered systems -- theory of electronic bands melting

TL;DR

This paper develops a theoretical framework to understand how strong disorder affects ARPES spectra, linking spectral broadening to disorder criticality and phase transitions, with a focus on a 2D frustrated spin model.

Contribution

It introduces a rigorous theory of ARPES in disordered systems, modifying the sudden approximation and connecting spectral broadening to disorder operator criticality.

Findings

ARPE spectra become invisible with increasing disorder

Spectral broadening linked to disorder operator criticality

Formalism applicable beyond the specific model studied

Abstract

It is well known that translational symmetry-breaking disorder will disrupt ARPES spectra up to the point where they become invisible. However, a theoretical framework to capture this phenomenon has been largely missing. Here, based on a rigorous theory of the ARPES process, we provide this much-needed framework. In particular, we show how the frequently used sudden electron approximation has to be modified in this situation. Our main result is an argument that links the photoemission line broadening with an operator content of a disorder operator and so with the criticality of the corresponding order-disorder phase transition. For concreteness, we focus here on the frustrated 2D trigonal (pseudo-)spin model, with Ising order-disorder operators behind the transition. Still, our formalism is general and can be applied in a much broader context.