Imaging phonon-mediated hydrodynamic flow in WTe2 with cryogenic quantum magnetometry

Hydrodynamic electron flow is a unique signature of strong electron interactions in a material. This effect has been observed in 2D materials, but observations in bulk materials are intriguing as high-carrier density should screen the interactions. In this work, we study hydrodynamic flow in the semimetal WTe2 to gain insight into the microscopic origin of its electron interactions.

We image the spatial profile of the electric current by using a nitrogen-vacancy scanning tip. Using coherent quantum sensing, we obtain magnetic field resolution of ~10nT and spatial resolution of ~100nm. The current pattern we observe differs substantially from the flat profile of a normal metal, and indicates correlated flow through the semimetal. The pattern also shows non-monotonic temperature dependence, with hydrodynamic effects peaking at ~20 K.

We compare our results to a model which combines ab initio electron scattering rates and the electronic Boltzmann transport equation.
The model shows quantitative agreement with our measurement, allowing us to extract the strength of electron-electron interactions in our material. Furthermore, we conclude that electron interactions are phonon-mediated. This result opens a path for hydrodynamic flow and strong interactions in a variety of new materials.