Anomalously Suppressed Thermal Conduction by Electron‐Phonon Coupling in Charge‐Density‐Wave Tantalum Disulfide

Charge and thermal transport in a crystal is carried by free electrons and phonons (quantized lattice vibration), the two most fundamental quasiparticles. Above the Debye temperature of the crystal, phonon‐mediated thermal conductivity (κ L) is typically limited by mutual scattering of phonons, which results in κ L decreasing with inverse temperature, whereas free electrons play a negligible role in κ L. Here, an unusual case in charge‐density‐wave tantalum disulfide (1T‐TaS2) is reported, in which κ L is limited instead by phonon scattering with free electrons, resulting in a temperature‐independent κ L. In this system, the conventional phonon–phonon scattering is alleviated by its uniquely structured phonon dispersions, while unusually strong electron‐phonon (e‐ph) coupling arises from its Fermi surface strongly nested at wavevectors in which phonons exhibit Kohn anomalies. The unusual temperature dependence of thermal conduction is found as a consequence of these effects. The finding reveals new physics of thermal conduction, offers a unique platform to probe e‐ph interactions, and provides potential ways to control heat flow in materials with free charge carriers. The temperature‐independent thermal conductivity may also find thermal management application as a special thermal interface material between two systems when the heat conduction between them needs to be maintained at a constant level.
Electron–phonon interaction that normally plays negligible role in lattice thermal conduction of crystalline materials is found to dominantly scatter phonons and limit thermal conduction in a charge‐density‐wave material, 1T‐TaS2. This work elucidates the basic transport behavior of the two most fundamental quasi‐particles in a crystal, free electrons and phonons.