Intrinsic Temporal Coherence Governs Heat Transport of Zone-Folded Phonons

TL;DR

This paper reveals that intrinsic temporal coherence of phonons significantly influences heat transport in superlattices, offering new insights beyond traditional spatial coherence models.

Contribution

It introduces the concept of temporal coherence as a key factor in phonon-mediated heat conduction, contrasting with prior focus on spatial coherence.

Findings

Intrinsic phonon coherence dominates heat transport in ultrashort-period superlattices.

Wigner transport equation shows minor effect of band folding on thermal conductivity.

Temperature dependence models with and without temporal coherence offer testable experimental predictions.

Abstract

While spatial phonon coherence manifested through band folding is believed to be a key factor governing the anomalous thermal conductivity of periodic structures, we investigate phonon transport from the perspective of temporal coherence. Using mode-resolved analyses, we quantify temporal coherent contributions and elucidate the interplay between phonon coherence time and lifetime in heat conduction of graphene/hexagonal boron nitride superlattices. We find that intrinsic coherence of folded phonon modes dominates the enhancement in ultrashort-period superlattices. In contrast, Wigner transport equation yields only a minor effect of band folding on thermal conductivity. The predictions in temperature dependence of models with and without temporal coherence provide a falsifiable experimental signature of this effect. Temporal coherence therefore constitutes a previously overlooked but fundamental channel for heat conduction, extending the conventional picture of spatially coherent transport and deepening the understanding of phonon dynamics in superlattices.