Assessing Phonon Coherence Using Spectroscopy

TL;DR

This paper develops a spectroscopy-based theoretical model to measure phonon coherence, validated by experiments and simulations, revealing size-dependent coherence behaviors crucial for understanding heat transport in solids.

Contribution

The paper introduces a novel theoretical framework for experimentally assessing phonon coherence using spectroscopy, bridging a gap in measurement methodologies.

Findings

Confined modes show higher coherence-to-lifetime ratios.

Phonon coherence depends on system size.

The model enables extracting coherence times from existing spectroscopy data.

Abstract

As a fundamental physical quantity of thermal phonons, temporal coherence participates in a broad range of thermal and phononic processes, while a clear methodology for the measurement of phonon coherence is still lacking. In this Lettter, we derive a theoretical model for the experimental exploration of phonon coherence based on spectroscopy, which is then validated by comparison with Brillouin light scattering data and direct molecular dynamic simulations of confined modes in nanostructures. The proposed model highlights that confined modes exhibit a pronounced wavelike behavior characterized by a higher ratio of coherence time to lifetime. The dependence of phonon coherence on system size is also demonstrated from spectroscopy data. The proposed theory allows for reassessing data of conventional spectroscopy to yield coherence times, which are essential for the understanding and the estimation of phonon characteristics and heat transport in solids in general.