Charge accumulation driven by pseudo-hydrodynamics of quasiparticles in a semimetal WTe₂ at room temperature

    Currently, the hydrodynamic behavior of carriers has been attracting much interest. For example, the ultraclean graphene can show a hydrodynamic charge flow, when momentum conserving carrier-carrier scattering is dominant than other scatterings, e.g. whirlpool structure similar with flowing water. The vortices indicates the back flow of the current resulting in a negative nonlocal voltage near current sources and drains. For example, the negative-positive-negative patterns in the voltage near the contacts can be utilize as an evidence of experimentally signature of the electronic viscous behavior.

    We directly image similar charge-alternating accumulation patterns in WTe₂ in the semimetallic phase at room temperature by adopting a polarization-sensitive laser microscopy method with an electrical bias. The spatial charge distribution shows extremely long relaxation length, ~1.4 μm, which are much more extended than a charge screening length in conventional semimetals (usually nanometer scales). We analyze that the phenomena are originated from the long recombination time of electron-hole pairs in this nearly-compensated Weyl semimetal.

    We theoretically suggest that these exotic charge accumulation behaviors appear due to the unbalanced diffusive flow of electron-hole currents. Our analytical calculations show that the Ohmic electric current can produce pseudo-hydrodynamic whirlpool structures in the charge neutral current. We argue that it is the backflow of a neutral current which leads to the exotic alternating charge distribution near the contacts. Moreover, the fluid-like behavior of the quasiparticle can be described in terms of a modified Navier-Stokes equation equipped with higher-derivative terms.