Current instability in a driven 2d electron liquid probed by nanoscale magnetometry

A moving fluid can become unstable in the presence of an obstruction, 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 that 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 through 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.  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 directional symmetry of the device as would be expected for a fluid instability seeded by disorder.  The combined global and local measurements indicate non-linear 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 phenomena.

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Bio:

Javier Sanchez-Yamagishi studies the behavior of electrons in 2-dimensional materials using electronic transport and nanoscale magnetometry.  He currently is a postdoctoral fellow at the Harvard Quantum Optics Center, working in the groups of Mikhail Lukin and Hongkun Park.  For his PhD work, he studied the quantum transport properties of graphene-based heterostructures in the group of Pablo Jarillo-Herrero at MIT.