[Paper Review] Intrinsic nonlinear Hall effect and gate-switchable Berry curvature sliding in twisted bilayer graphene

Meizhen Huang, Zefei Wu+9 more|arXiv (Cornell University)|Dec 24, 2022

Graphene research and applications4 citations

TL;DR

This study demonstrates an intrinsic nonlinear Hall effect in high-quality twisted bilayer graphene driven by a Berry curvature dipole, with gate-tunable control over the nonlinear Hall response via displacement field-induced sliding of Berry curvature hotspots. The results confirm the dominance of intrinsic topology over extrinsic disorder in nonlinear transport and establish twisted bilayer graphene as a tunable platform for nonlinear Hall effects and second-harmonic generation.

ABSTRACT

Though the observation of the quantum anomalous Hall effect and nonlocal transport response reveals nontrivial band topology governed by the Berry curvature in twisted bilayer graphene, some recent works reported nonlinear Hall signals in graphene superlattices that are caused by the extrinsic disorder scattering rather than the intrinsic Berry curvature dipole moment. In this work, we report a Berry curvature dipole induced intrinsic nonlinear Hall effect in high-quality twisted bilayer graphene devices. We also find that the application of the displacement field substantially changes the direction and amplitude of the nonlinear Hall voltages, as a result of a field-induced sliding of the Berry curvature hotspots. Our work not only proves that the Berry curvature dipole could play a dominant role in generating the intrinsic nonlinear Hall signal in graphene superlattices with low disorder densities, but also demonstrates twisted bilayer graphene to be a sensitive and fine-tunable platform for second harmonic generation and rectification.

Motivation & Objective

• To distinguish intrinsic Berry curvature dipole contributions from extrinsic disorder effects in nonlinear Hall responses in graphene superlattices.
• To investigate the role of band topology in generating nonlinear Hall signals in high-quality twisted bilayer graphene devices.
• To explore the tunability of nonlinear Hall effects via external electric fields in twisted bilayer graphene.
• To demonstrate the dynamic control of Berry curvature distribution through gate voltage in twisted bilayer graphene.
• To establish twisted bilayer graphene as a platform for gate-switchable second harmonic generation and rectification.

Proposed method

• Measurement of nonlinear Hall voltage in exfoliated twisted bilayer graphene devices with low disorder density.
• Application of a perpendicular displacement field to tune the band structure and Berry curvature distribution.
• Use of transport measurements to extract the nonlinear Hall conductance and its field dependence.
• Analysis of the Berry curvature dipole moment as the origin of the intrinsic nonlinear Hall effect.
• Observation of directional and amplitude modulation of nonlinear Hall voltage with gate voltage, indicating Berry curvature hotspot sliding.
• Comparison of experimental results with theoretical models of intrinsic nonlinear response in topological systems.

Experimental results

Research questions

• RQ1 Can the intrinsic Berry curvature dipole generate a dominant nonlinear Hall effect in high-quality twisted bilayer graphene, independent of disorder?
• RQ2 How does the displacement field alter the spatial distribution and strength of Berry curvature in twisted bilayer graphene?
• RQ3 To what extent can the nonlinear Hall voltage be tuned in magnitude and direction using gate voltage?
• RQ4 What is the role of Berry curvature hotspot sliding in modulating the nonlinear Hall response?
• RQ5 Can twisted bilayer graphene serve as a gate-switchable platform for second harmonic generation and rectification?

Key findings

• The intrinsic nonlinear Hall effect in twisted bilayer graphene is dominated by the Berry curvature dipole, not extrinsic disorder scattering.
• The application of a displacement field induces a measurable sliding of Berry curvature hotspots, altering the direction and amplitude of the nonlinear Hall voltage.
• The nonlinear Hall voltage exhibits strong gate-tunability, with reversible switching of sign and magnitude observed under varying displacement fields.
• The observed nonlinear Hall response is consistent with theoretical predictions of Berry curvature dipole-driven transport in topological systems.
• The system demonstrates gate-switchable second harmonic generation and rectification, highlighting its potential for nonlinear nanoelectronics.
• The results confirm that high-quality twisted bilayer graphene supports robust, tunable nonlinear responses rooted in intrinsic topology.