Observation of Cavity-Mediated Nonlinear Landau Fan and Modified Landau Level Degeneracy in Graphene Quantum Transport

TL;DR

This study demonstrates how ultra-strong coupling between a terahertz cavity and graphene alters Landau level degeneracies, affecting quantum Hall features and revealing cavity-induced modifications in 2D electron systems.

Contribution

It shows that cavity vacuum fields can modify Landau level degeneracies in graphene, enabling control over quantum Hall phenomena through cavity quantum electrodynamics.

Findings

Quantum Hall features occur at lower carrier densities with cavity coupling.

Cavity vacuum fields alter the effective degeneracies of Landau levels.

Theoretical analysis links virtual photon transitions to degeneracy reduction.

Abstract

Recent studies on cavity-coupled two-dimensional electron gas demonstrate that vacuum-field engineering can tailor electronic transport properties of materials. By achieving ultra-strong coupling between a terahertz resonator and mesoscopic graphene, we demonstrate that cavity vacuum fields can alter the effective degeneracies of Landau levels, resulting in a nonlinear Landau fan diagram for massless Dirac fermions while preserving quantum-Hall quantization. Specifically, by leveraging graphene's gate-tunability, we observe that quantum-Hall features, minimum longitudinal and quantized Hall conductance for a given filling factor, occur at carrier densities reduced by more than 20 percent compared to systems without cavity. Theoretical analysis attributes this effect to the virtual cavity photon mediated transitions between the non-equidistant Landau levels in graphene, significantly reducing their effective degeneracy. This study paves the way for investigating cavity quantum electrodynamics in highly tunable, atomically thin two-dimensional crystals.