Terahertz magneto-nanoscopy of encapsulated monolayer graphene

Abstract

This study investigates the nanoscale conductivity of encapsulated monolayer graphene at temperatures down to 5 K and magnetic fields of up to 1 T. We use the scattering-type scanning near-field optical microscopy (s-SNOM) technique to probe magnetic-field-dependent responses from graphene close to charge neutrality in the terahertz spectral region. We observe the near-perfect high-$q$ reflector behavior of graphene but with subtle changes by the presence of magnetic fields. Measurements align with calculations of the magneto-optical conductivity and the near-field spectroscopic contrast that describes the field-tunable cyclotron resonance of Dirac fermions. Our result provides an initial step toward understanding temperature and magnetic-field effects on nanoscale terahertz transport in two-dimensional quantum materials.