ABC...z Seminar Series: Thursday, January 18th: Current instability in a driven 2d electron liquid probed by nanoscale magnetometry

Event Date: 

Thursday, January 18, 2018 - 3:45pm

Event Date Details: 

Refreshments served at 3:30pm.

Event Location: 

  • 1605 Elings Hall
  • ABC...z Seminar Series

A moving fluid can become unstable in the presence of an obstruction or temperature gradient, leading to a flow pattern that fluctuates in time. Such collective nonlinear dynamics are a distinct feature of fluids, in contrast to the uncorrelated behavior of a non-interacting system. It has been recently found that some materials, such as graphene, host electrons which behave like a collective fluid. Experiments have demonstrated linear hydrodynamic phenomena, such as viscous drag at sample boundaries, but nonlinear effects have yet to be reported. We observe a AC current instability that develops when driving a DC current bias in a graphene device in the electron hydrodynamic regime. The current fluctuations are larger than typical electronic noise and broadly peaked in the ~Ghz frequency range. The instability is strongly enhanced at cryogenic temperatures, and is suppressed at low carrier density. To probe the local structure of the instability, we use diamond NV magnetometry to measure the current fluctuations at the nanoscale. We find that the current fluctuations vary strongly across the sample. Remarkably, some regions exhibit fluctuations that are strongly dependent on the direction of the current, breaking the assumed directional symmetry of the device. This asymmetry pattern inverts when changing the carrier sign, indicating that it is dependent on the direction of carrier flow, as would be expected for a fluid instability seeded by disorder. The combined global and local measurements of the current fluctuations indicates nonlinear effects which arise when driving the graphene electron liquid. In addition, this work demonstrates the power of using local magnetometry probes in combination with traditional global measurements to gain deeper insight into electronic behaviors.

Javier Sanchez-Yamagishi, Harvard University