Quantum frequency doubling in the topological insulator Bi₂Se₃

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Nonlinear Hall effect and frequency doubling were previously linked to Berry curvature dipole (BCD) in time-reversal-invariant materials.
• Topological insulators possess unique surface states with inherent chirality.

Purpose of the Study:

• To investigate electric frequency doubling in topological insulators without BCD.
• To identify the underlying mechanism responsible for this novel nonlinear electric effect.

Main Methods:

• Experimental observation of transverse voltage in response to AC current on Bi2Se3 surface.
• Symmetry analysis to distinguish between BCD and other mechanisms.
• Theoretical introduction of Berry curvature triple to explain skew scattering.

Main Results:

• Observed electric frequency doubling on the surface of Bi2Se3 under zero magnetic field, independent of BCD.
• The frequency-doubling voltage exhibited threefold rotational symmetry, inconsistent with BCD.
• Identified skew scattering, originating from the topological surface state's chirality, as the dominant mechanism.

Conclusions:

• Demonstrated a novel route to electric frequency doubling in topological insulators by harnessing skew scattering.
• Introduced the Berry curvature triple as a key concept for understanding high-order nonlinear effects.
• This finding opens avenues for developing giant second-order nonlinear electric effects in high-mobility quantum materials.