Generalized Design Principles for Hydrodynamic Electron Transport in Anisotropic Metals

TL;DR

This paper develops general principles for realizing hydrodynamic electron transport in anisotropic metals, supported by ab initio calculations on specific semimetals, broadening the scope of materials where such phenomena can be observed.

Contribution

It introduces analytical and computational criteria for identifying materials capable of exhibiting hydrodynamic electron flow, emphasizing the role of electron-phonon interactions and anisotropy.

Findings

Hydrodynamic regime can occur in a wider class of anisotropic metals.

Materials with strong electron-phonon interactions are promising candidates.

Layered and anisotropic semimetals with specific electronic structures are ideal for observing hydrodynamics.

Abstract

Interactions of charge carriers with lattice vibrations, or phonons, play a critical role in unconventional electronic transport of metals and semimetals. Recent observations of phonon-mediated collective electron flow in bulk semimetals, termed electron hydrodynamics, present new opportunities in the search for strong electron-electron interactions in high carrier density materials. Here we present the general transport signatures of such a second-order scattering mechanism, along with analytical limits at the Eliashberg level of theory. We study electronic transport, using $ab$ $initio$ calculations, in finite-size channels of semimetallic ZrSiS and TaAs$_2$ with and without topological band crossings, respectively. The order of magnitude separation between momentum-relaxing and momentum-conserving scattering length-scales across a wide temperature range make both of them promising candidates for further experimental observation of electron hydrodynamics. More generally, our calculations show that the hydrodynamic transport regime can be realized in a much broader class of anisotropic metals and does not, to first order, rely on the topological nature of the bands. Finally, we discuss general design principles guiding future search for hydrodynamic candidates, based on the analytical formulation and our $ab$ $initio$ predictions. We find that systems with strong electron-phonon interactions, reduced electronic phase space, and suppressed phonon-phonon scattering at temperatures of interest are likely to feature hydrodynamic electron transport. We predict that layered and/or anisotropic semimetals composed of half-filled $d$-shells and light group V/VI elements with lower crystal symmetry are ideal candidates to observe hydrodynamic phenomena in future.