Abstract
The flow of charge and entropy in solids usually depends on collisions decaying quasiparticle momentum. Hydrodynamic corrections can emerge, however, if most collisions among quasiparticles conserve momentum and the mean-free path approaches the sample dimensions. Here, through a study of electrical and thermal transport in antimony (Sb) crystals of various sizes, we document the emergence of a two-component fluid of electrons and phonons. Lattice thermal conductivity is dominated by electron scattering down to 0.1 K and displays prominent quantum oscillations. The Dingle mobility does not vary despite an order-of-magnitude change in transport mobility. The Bloch-Grüneisen behavior of electrical resistivity is suddenly aborted below 15 K and replaced by a quadratic temperature dependence. At the Kelvin temperature range, the phonon scattering time and the electron-electron scattering time display a similar amplitude and temperature dependence. Taken together, the results draw a consistent picture of a bifluid where frequent momentum-conserving collisions between electrons and phonons dominate the transport properties.
- Received 11 January 2022
- Revised 1 April 2022
- Accepted 7 June 2022
DOI:https://doi.org/10.1103/PhysRevX.12.031023
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
The thermal conductivity of a solid usually depends on the rate of collisions imposed on carriers of heat: phonons and mobile electrons. Collisions that decay momentum degrade the heat flow, but collisions that conserve momentum do not. In any solid, electrons and phonons can experience either type of collision; which type depends on temperature. Usually at low temperature, phonons become ballistic and do not lose momentum in collisions. In this study, we show that this is not the case in antimony at cryogenic temperatures. Rather, the heat carried by the phonon flow leaks through its tight coupling to the electron flow.
Using measurements of electrical resistivity and thermal conductivity over a range of cryogenic temperatures, we show that phonons in elemental antimony collide more frequently with electrons than with other phonons. By losing their momentum to electrons through these collisions, phonons have a mean-free path that is much shorter than the sample size. The electron-phonon momentum exchange becomes asymmetric: Phonon-phonon collisions conserve momentum whereas many electron-electron collisions do not. This electron-phonon exchange happens much less in antimony (with one electron per 1000 atoms) than it does in copper (roughly one electron per atom) but often enough to make antimony different from insulators.
Therefore, in this cryogenic temperature range, what degrades the flow of charge and heat in antimony are collisions of electrons with other electrons, defects, and boundaries. Such a picture of electron-phonon bifluidity, where frequent collisions between the electronic and phononic quasiparticles dominate transport, may be relevant to other solids of comparable carrier concentration.
