Yuxiang Ni | Searcharxiv

arXiv2026

Intrinsic Temporal Coherence Governs Heat Transport of Zone-Folded Phonons

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.

cond-mat.mes-hall↗

arXiv2015

Functionalization mediates heat transport in graphene nanoflakes

Self-heating is a severe problem for high-power microelectronic devices. Graphene and few-layer graphene have attracted tremendous attention for heat removal thanks to their extraordinarily high in-plane thermal conductivity. However, this high thermal conductivity undergoes severe degradations caused by the contact with the substrate and the functionalization-induced point defects. Here we show that thermal management of a micro heater can be substantially improved via introduction of alternative heat-escaping channels implemented with graphene-based film covalently bonded to functionalized graphene oxide through silane molecules. Theoretical and experimental results demonstrate a counter-intuitive enhancement of the thermal conductivity of such a graphene-based film. This increase in the in-plane thermal conductivity of supported graphene is accompanied by an improvement on the graphene-substrates thermal contact. Using infrared thermal imaging, we demonstrate that the temperature of the hotspots can be lowered by 12 $^o$C in transistors operating at 130 W mm$^{-2}$ , which corresponds to half of an order-of-magnitude increase in the device lifetime. Ab initio and molecular dynamics simulations reveal that the functionalization constrains the cross-plane scattering of low frequency phonons, which in turn enhances in-plane heat conduction of the bonded graphene film by recovering the long flexural phonon lifetime.

cond-mat.mes-hall↗