Electron-phonon coupled hydrodynamics in semimetal TaAs_2

Shan Jiang; Wei Xie; Xiaokang Li; Kamran Behnia; Zengwei Zhu

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arXiv · 2609.03517

Electron-phonon coupled hydrodynamics in semimetal TaAs_2

Shan Jiang·Wei Xie·Xiaokang Li·Kamran Behnia·Zengwei Zhu

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Abstract

Hydrodynamic corrections to diffusive transport can arise when momentum-conserving collisions between quasiparticles become prominent, and they have been documented for both electrons and phonons. An emerging frontier topic is coupled electron-phonon (e-ph) hydrodynamics. Here, through electrical and thermal transport measurements on TaAs2 crystals with different impurity levels, we document the emergence of an e-ph bifluid in the temperature window of 5 to 15 K. Within this range, the lattice thermal conductivity exhibits a faster-than-T^3 temperature dependence, as a consequence of non-monotonic and purity-dependent phonon mean free paths, a signature of phonon Poiseuille flow. However, strong e-ph coupling impedes the emergence of a ballistic regime. This is corroborated by the observation of quantum oscillations in the lattice thermal conductivity. Prominent phonon-mediated momentum exchange between electrons amplifies the violation of the Wiedemann-Franz law and yields a two-order-of-magnitude discrepancy between quantum and transport lifetimes, a signature of electron hydrodynamics in semimetals. Our results imply that in semimetals with optimized e-ph coupling, thanks to matching between the cryogenic phonon wave?length and the Fermi wavelength, momentum and energy flow between the electron and phonon reservoirs as frequently as within each reservoir.

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Shan Jiang, Wei Xie, Xiaokang Li, Kamran Behnia, Zengwei Zhu. 2026-09-03. Electron-phonon coupled hydrodynamics in semimetal TaAs_2. https://arxiv.org/abs/2609.03517

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