Low Magnetic Field Regime of a Gate-Defined Constriction in High-Mobility Graphene

TL;DR

This study explores how electronic transport in a high-mobility graphene constriction transitions from ballistic to quantum Hall regimes as magnetic field increases, revealing Fabry-Pérot resonances, snake trajectories, and Landau level effects.

Contribution

It provides detailed experimental and numerical analysis of magnetic field effects on coherent transport in graphene constrictions, highlighting the transition from Fabry-Pérot to quantum Hall phenomena.

Findings

Fabry-Pérot resonances at low magnetic fields

Snake trajectories guiding conductance oscillations at intermediate fields

Landau level spectrum distortions at high magnetic fields

Abstract

We report on the evolution of the coherent electronic transport through a gate-defined constriction in a high-mobility graphene device from ballistic transport to quantum Hall regime upon increasing the magnetic field. At low field, the conductance exhibits Fabry-P\'erot resonances resulting from the npn cavities formed beneath the top-gated regions. Above a critical field $B^*$ corresponding to the cyclotron radius equal to the npn cavity length, Fabry-P\'erot resonances vanish and snake trajectories are guided through the constriction with a characteristic set of conductance oscillations. Increasing further the magnetic field allows us to probe the Landau level spectrum in the constriction, with distortions due to the combination of confinement and de-confinement of Landau levels in a saddle potential. These observations are confirmed by numerical calculations.