  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 conducting channels, polynomial
scaling of the resistance as a function of the channel width, substantial
violation of the Wiedemann-Franz law supported by the emergence of the
Poiseuille flow. Similarly to whirlpools in flowing water, the viscous
electronic flow generates vortices, resulting in abnormal sign-changing
electrical response driven by the backflow of electrical current.
Experimentally, the presence of the hydrodynamic vortices was observed in
low-temperature graphene as a negative voltage drop near the current-injecting
contacts. 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 we use polarization-sensitive laser microscopy
to demonstrate the emergence of visually similar abnormal sign-alternating
patterns in charge density in multilayer tungsten ditelluride at room
temperature where this material does not exhibit true electronic hydrodynamics.
We argue that this pseudo-hydrodynamic behavior appears due to a subtle
interplay between the diffusive transport of electrons and holes. In
particular, the sign-alternating charge accumulation in WTe2 is supported by
the unexpected backflow of compressible neutral electron-hole current, which
creates charge-neutral whirlpools in the bulk of this nearly compensated
semimetal. We demonstrate that the exceptionally large spatial size of the
charge domains is sustained by the long recombination time of electron-hole
pairs.
