Tunable and giant valley-selective Hall effect in gapped bilayer graphene

TL;DR

This paper demonstrates a tunable valley-selective Hall effect in gapped bilayer graphene, showing large, controllable Hall voltages via electric fields and optical excitation, with implications for advanced quantum electronic devices.

Contribution

It reports the first in situ tunable valley-selective Hall effect in bilayer graphene, linking Berry curvature control to electric fields and optical methods, surpassing effects in other materials.

Findings

Valley-selective Hall effect is tunable by out-of-plane electric field.

Observed Hall voltages are significantly larger than in molybdenum disulfide.

Berry curvature scales inversely with bandgap, affecting the Hall effect.

Abstract

Berry curvature is analogous to magnetic field but in momentum space and is commonly present in materials with non-trivial quantum geometry. It endows Bloch electrons with transverse anomalous velocities to produce Hall-like currents even in the absence of a magnetic field. We report the direct observation of in situ tunable valley-selective Hall effect (VSHE), where inversion symmetry, and thus the geometric phase of electrons, is controllable by an out-of-plane electric field. We use high-quality bilayer graphene with an intrinsic and tunable bandgap, illuminated by circularly polarized mid-infrared light and confirm that the observed Hall voltage arises from an optically-induced valley population. Compared with molybdenum disulfide, we find orders of magnitude larger VSHE, attributed to the inverse scaling of the Berry curvature with bandgap. By monitoring the valley-selective Hall conductivity, we study Berry curvature's evolution with bandgap. This in situ manipulation of VSHE paves the way for topological and quantum geometric opto-electronic devices, such as more robust switches and detectors.