Quasilocalized Vibrational Modes as Efficient Heat Carriers in Glasses

TL;DR

This study demonstrates that soft quasilocalized vibrational modes in glasses, despite their localized nature, are highly effective in conducting heat at low temperatures, challenging previous assumptions about their role in thermal transport.

Contribution

We reveal that low-frequency quasilocalized modes significantly contribute to thermal conductivity in glasses, driven by their mutual coherence with other vibrational modes.

Findings

Quasilocalized modes are effective heat carriers at low temperatures.

High thermal exchange is due to coherence between modes.

These modes contribute notably to thermal conductivity below 0.05 Tg.

Abstract

While soft quasilocalized vibrational modes are known to populate the low-frequency spectrum of glassy solids, their contribution to thermal properties is still not fully elucidated. We numerically show that, despite their spatially localized nature, these modes are as effective heat carriers as the delocalized ones and can contribute non-negligible to the total thermal conductivity in the low-temperature regime, especially for T < 0.05 Tg where Tg is the glass transition temperature. We further prove that the mutual coherence between the low-frequency quasilocalized modes and other modes explains this high thermal exchange performance. Our finding finally provides a perspective on the thermal transport behaviour of the low-frequency quasilocalized modes in glassy solids.