Phonon Dichroisms Revealing Unusual Electronic Quantum Geometry

TL;DR

This paper uncovers how quantum geometry influences phonon dichroisms in solids with broken symmetries, linking electronic quantum properties to observable phonon behaviors and proposing experimental detection methods.

Contribution

It reveals the quantum-geometric origin of phonon dichroisms and introduces the heat magnetic moment as a key factor, supported by a model system demonstration.

Findings

Circular phonon dichroism dominated by heat magnetic moments

Linear phonon dichroism depends on heat Drude weight

Established f-sum rule for heat magnetic moment detection

Abstract

The quantum geometry tensor, intrinsic geometric characteristics of electronic states, plays a crucial role in the various nontrivial electromagnetic phenomena in quantum materials. Here, we reveal that quantum geometry significantly modifies phonon dichroisms through electron-phonon interactions in solids that break time-reversal and spatial inversion symmetries. Specifically, the circular phonon dichroism is primarily dominated by the heat magnetic moments, while the linear phonon dichroism depends on the heat Drude weight, a thermal analog of band Drude weight. Furthermore, we establish the f-sum rule for the heat magnetic moment that facilitates its experimental detections. We demonstrate our key findings in an archetypal model system: ferromagnetic two-dimensional electron gases with Rashba spin-orbit coupling. Our work uncovers the quantum-geometric origin of common phonon dichroisms and predicts the detectable signature of the heat magnetic moment of electrons in solids.