Pseudo‐Hydrodynamic Flow of Quasiparticles in Semimetal WTe2 at Room Temperature

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 19; no. 27; pp. e2206604 - n/a
• Main Authors: Choi, Young‐Gwan, Doan, Manh‐Ha, Ngoc, Luu Ly Pham, Lee, Junsu, Choi, Gyung‐Min, Chernodub, Maxim Nikolaevich
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.07.2023; Wiley-VCH Verlag
• Subjects: Charge transport; Condensed Matter; Electrons; Elementary excitations; Fluid flow; Fluid mechanics; High Energy Physics - Phenomenology; Hydrodynamics; Laminar flow; Laser microscopy; Nanotechnology; Physics; Polynomials; quasi‐particles; Room temperature; Strongly Correlated Electrons; WTe2
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202206604

Recently, much interest has emerged in fluid‐like electric charge transport in various solid‐state systems. The hydrodynamic behavior of the electronic fluid reveals itself as a decrease of the electrical resistance with increasing temperature (the Gurzhi effect) in narrow channels, polynomial scaling of the resistance as a function of the channel width, violation of the Wiedemann–Franz law supported by the emergence of the Poiseuille flow. Similar to whirlpools in flowing water, the viscous electronic flow generates vortices, resulting in abnormal sign‐changing electrical response driven by backflow. However, the question of whether the long‐ranged sign‐changing electrical response can be produced by a mechanism other than hydrodynamics has not been addressed so far. Here polarization‐sensitive laser microscopy is used to demonstrate the emergence of visually similar abnormal sign‐alternating patterns in semi‐metallic tungsten ditelluride at room temperature where this material does not exhibit true hydrodynamics. It is found that the neutral quasiparticle current consisting of electrons and holes obeys an equation remarkably similar to the Navier–Stokes equation. In particular, the momentum relaxation is replaced by the much slower process of quasiparticle recombination. This pseudo‐hydrodynamic flow of quasiparticles leads to a sign‐changing charge accumulation pattern via different diffusivities of electrons and holes. Using polarization‐sensitive laser microscopy, the distinctive sign‐alternating patterns of electric charge density generated by electric current in room‐temperature semimetal WTe2 are observed. Strong evidence is provided that this abnormal phenomenon, unexpected at room temperature, is produced by whirlpools of the compressible flow of neutral electron–hole quasi‐particles. The immense spatial size of the charge domain is sustained by the long recombination time of electron–hole pairs in this nearly compensated material.