Abstract
Charge transport of topological semimetals is the focus of intensive investigations because of their nontrivial band topology. Heat transport of these materials, on the other hand, is largely unexplored and remains elusive. Here, we report on an observation of unprecedented, giant magnetic quantum oscillations of thermal conductivity in the prototypical Weyl semimetal TaAs. The oscillations are antiphase with the quantum oscillating electronic density of states of a Weyl pocket, and their amplitudes amount to 2 orders of magnitude of the estimation based on the Wiedemann-Franz law. Our analyses show that all the conventional heat-transport mechanisms through diffusions of propagating electrons, phonons, and electron-hole bipolar excitations are far inadequate to account for these phenomena. Taking further experimental facts that the parallel field configuration favors much-higher magnetothermal conductivity, we propose that the newly proposed chiral zero sound provides a reasonable explanation to these exotic phenomena. More work focusing on other topological semimetals along the same line is badly called for.
- Received 9 February 2019
- Revised 16 July 2019
DOI:https://doi.org/10.1103/PhysRevX.9.031036
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
In solids, heat conduction is mediated by propagating electrons and phonons. A good heat conductor is usually a good electrical conductor, too. However, researchers have yet to figure out if this correspondence between heat and electrical conductance holds for topological semimetals, which are regarded as superior electrical conductors with relativistic electrons. Here, we report on unprecedented giant magnetic quantum oscillations of heat conduction in a type of topological semimetal known as a Weyl semimetal. This behavior cannot be explained by moving electrons or phonons, but instead appears to arise from chiral zero sound, a newly discovered heat transport mechanism seen in Weyl semimetals.
To study the connection between heat and electrical conduction, we take samples of the Weyl semimetal TaAs and measure how heat conduction, in comparison with electrical conduction, responds to magnetic field. Except for the well-known quantum oscillations in the latter, surprisingly, we observe an unprecedented, largely oscillatory heat conduction as a function of magnetic field. The oscillations of heat transport are so large that they go far beyond the expected heat carried by propagating electrons. Furthermore, the observed unique heat transport prefers to flow along the direction of the magnetic field. All these observations match the expected behaviors of chiral zero sound, a new acoustic vibration mode carried by Weyl electrons.
Our results will motivate further studies of unconventional heat conduction in topological materials. Along with the superior electrical transport, this new heat transport mechanism may help to find feasible applications of topological semimetals.