Tracking flat bands via phonon-mediated interband scattering

Abstract

Flat-band (FB) materials have emerged as promising platforms for exploring exotic quantum phases. While numerous candidates have recently been identified through spectroscopic techniques such as angle-resolved photoemission spectroscopy, central challenges remain on how to tune FBs towards the Fermi level EF and to understand their impact on low-energy excitations probed in electronic transport experiments. Here, we show that, by attributing the temperature dependence of the electrical resistivity at elevated temperatures to electron-phonon interband scattering, one can infer the position of FBs near EF across diverse material classes. As charge carriers scatter off phonons, interband transitions into FB states lead to distinctive sub- or superlinear resistivity at elevated temperatures, governed by the proximity of the FB to EF. Our phenomenological model captures these universal transport behaviors observed across several recently studied FB compounds and offers a simple, broadly applicable method for detecting flat bands.