Experimental observation of hydrodynamic-like behavior in 3D Dirac semimetal ZrTe5.

Hydrodynamic fluidity in condensed matter physics has been experimentally demonstrated only in a limited number of compounds because of the stringent conditions that must be satisfied. Herein, we demonstrate the existence of hydrodynamic-like properties driven by the collective excitation of the Dirac fluid in the three-dimensional topological semimetal ZrTe5. By measuring the electrical and thermal properties in a wide temperature range, we find a regime satisfying phononic hydrodynamic-like characteristics with two representative experimental evidences: a faster evolution of the thermal conductivity than in the ballistic regime and the existence of a local maximum of the effective mean free path. In contrast to phononic hydrodynamics, the Wiedemann-Franz law is violated by about a factor of 100. Moreover, phonon-dragged anomalies are observed, which serve as a signature of the Dirac fluidity in this system.