Evidence for Local Spots of Viscous Electron Flow in Graphene at Moderate Mobility

Abstract

Dominating electron−electron scattering enables viscous electron flow exhibiting hydrodynamic current density patterns, such as Poiseuille profiles or vortices. The viscous regime has recently been observed in graphene by nonlocal transport experiments and mapping of the Poiseuille profile. Herein, we probe the current-induced surface potential maps of graphene field-effect transistors with moderate mobility using scanning probe microscopy at room temperature. We discover micrometer-sized large areas appearing close to charge neutrality that show currentinduced electric fields opposing the externally applied field. By estimating the local scattering lengths from the gate dependence of local in-plane electric fields, we find that electron−electron scattering dominates in these areas as expected for viscous flow. Moreover, we suppress the inverted fields by artificially decreasing the electron-disorder scattering length via mild ion bombardment. These results imply that viscous electron flow is omnipresent in graphene devices, even at moderate mobility.

Pseudo‐Hydrodynamic Flow of Quasiparticles in Semimetal WTe2 at Room Temperature

“…[6] The hydrodynamic flow of electrons can lead to a nonlocal macroscopic signature of viscosity. [7][8][9][10] In graphene, in addition to other striking signatures, [11][12][13][14][15][16][17][18][19][20][21][22] a localized injection of the electronic current creates whirlpools in the electron flow, thus resembling a classical fluid. [7,10] The whirlpools drive the electric current against the applied electric field, resulting in a negative nonlocal voltage near narrow electrodes.…”

Imaging the breaking of electrostatic dams in graphene for ballistic and viscous fluids

“…And, very recently, a scanned SQUID (superconducting quantum interference device) imaging technique has enabled visualization of current whirlpools in tungsten ditelluride ( 42 ). Lastly, Kelvin probe force microscopy has been used to image, with 60-nm resolution, regions of negative local resistance in chemical vapor–deposited graphene on silicon dioxide that were attributed to viscous flow behavior around intrinsic defects ( 43 ).…”

Valley hydrodynamics in gapped graphene

“…In fact, many pieces of clear evidence for hydrodynamic behaviors of charge carriers have been provided on graphene [32][33][34][35][36][37][38][39][40][41][42][43][44][45]. These nonequilibrium behaviors of interacting systems close to equilibrium are well described by tracking the evolution of conserved quantities including internal microscopic DOF.…”