Anomalous Thermal Transport Reveals Weak First-Order Melting of Charge Density Waves in 2H-TaSe2

TL;DR

This study uses thermal transport measurements to uncover persistent charge-density-wave fluctuations and weak first-order melting in 2H-TaSe2, revealing complex phase transition dynamics.

Contribution

It demonstrates that thermal conductivity can sensitively detect hidden CDW fluctuations and elucidate the nature of phase melting in layered quantum materials.

Findings

Thermal conductivity shows a V-shaped temperature dependence.

Persistent local CDW correlations exist up to at least 300 K.

Evidence of weak first-order melting of the CDW state.

Abstract

How ordered phases melt in low-dimensional quantum materials remain difficult to resolve because the relevant fluctuations are dynamic and charge neutral. In this work, we show that thermal transport provides a sensitive probe of these hidden fluctuations in the layered transition metal dichalcogenide 2H-TaSe2. We observe a striking V-shaped temperature dependence of the thermal conductivity that cannot be explained by conventional phonon-phonon scattering. Instead, it originates from scattering by persistent local charge-density-wave (CDW) correlations, consistent with our phenomenological model linking thermal transport to spatial CDW fluctuation. Electron diffraction reveals short-range periodic lattice distortions persisting to at least 300 K, while X-ray diffraction shows thermal hysteresis of the CDW wavevector. Together, these results reveal a dislocation- and fluctuation-driven weak first-order melting of the CDW state.