A tunable room-temperature nonlinear Hall effect in elemental bismuth thin films

The nonlinear Hall effect with time-reversal symmetry is a second-order electronic transport phenomenon-seen as a quadratic voltage transverse to an applied electric field-that induces frequency doubling and occurs in non-centrosymmetric crystals with large Berry curvature. Optoelectronic devices based on this effect are limited because it typically appears at low temperatures and in complex compounds characterized by Dirac or Weyl electrons. Here we report a room-temperature nonlinear Hall effect in polycrystalline thin films of the centrosymmetric elemental material bismuth. The electrons at the (111) surface possess a Berry curvature triple that activates side jumps and skew scatterings, which generate nonlinear transverse currents. We show that the zero-field nonlinear transverse voltage can be boosted in arc-shaped bismuth stripes due to an extrinsic geometric classical counterpart of the nonlinear Hall effect. The electrical frequency doubling in curved geometries can be extended to optical second-harmonic generation in the terahertz spectral range. We also demonstrate efficient third-harmonic generation in polycrystalline bismuth films and bismuth-based heterostructures across a broad range of terahertz frequencies.Polycrystalline thin films of elemental bismuth exhibit a room-temperature nonlinear transverse voltage due to geometric effects of surface electrons that is tunable and can be extended to efficient high-harmonic generation at terahertz frequencies.