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

Area of Science:

• Condensed Matter Physics
• Quantum Geometry
• Materials Science

Background:

• Berry curvature, analogous to magnetic fields in momentum space, drives anomalous velocities in Bloch electrons.
• This quantum geometric property enables Hall-like currents without external magnetic fields, particularly in materials with nontrivial band structures.

Purpose of the Study:

• To directly observe and tune the valley-selective Hall effect (VSHE) in situ.
• To investigate the influence of an electric field on inversion symmetry and electron geometric phase.
• To explore the relationship between bandgap, Berry curvature, and VSHE magnitude.

Main Methods:

• Utilized high-quality bilayer graphene with a tunable bandgap.
• Employed circularly polarized mid-infrared light illumination.
• Applied an out-of-plane electric field to control inversion symmetry.

Main Results:

• Achieved in situ, electric-field-tunable VSHE.
• Observed that the Hall voltage originates from optically induced valley population.
• Demonstrated significantly larger VSHE in bilayer graphene compared to MoS2, linked to inverse bandgap scaling of Berry curvature.

Conclusions:

• In situ manipulation of VSHE is demonstrated, offering control over electron geometric phase.
• The findings highlight the potential of bilayer graphene for enhanced optoelectronic applications.
• This work paves the way for topological and quantum geometric optoelectronic devices like switches and detectors.