Quantum frequency doubling in the topological insulator Bi2Se3

TL;DR

This paper reports a novel electric frequency doubling effect in Bi2Se3 topological insulator surfaces, driven by skew scattering and Berry curvature triple, independent of Berry curvature dipole, with potential for high nonlinear responses.

Contribution

It introduces the concept of Berry curvature triple and demonstrates frequency doubling without Berry curvature dipole in topological insulators.

Findings

Frequency doubling observed with threefold rotational symmetry.

Skew scattering identified as the underlying mechanism.

Potential for giant second-order nonlinear effects in quantum materials.

Abstract

The nonlinear Hall effect due to Berry curvature dipole (BCD) induces frequency doubling, which was recently observed in time-reversal-invariant materials. Here we report novel electric frequency doubling in the absence of BCD on a surface of the topological insulator Bi2Se3 under zero magnetic field. We observe that the frequency-doubling voltage transverse to the applied ac current shows a threefold rotational symmetry, whereas it forbids BCD. One of the mechanisms compatible with the symmetry is skew scattering, arising from the inherent chirality of the topological surface state. We introduce the Berry curvature triple, a high-order moment of the Berry curvature, to explain skew scattering under the threefold rotational symmetry. Our work paves the way to obtain a giant second-order nonlinear electric effect in high mobility quantum materials, as the skew scattering surpasses other mechanisms in the clean limit.