Detection of graphene's divergent orbital diamagnetism at the Dirac point

TL;DR

This study experimentally confirms the divergent orbital diamagnetism at the Dirac point in graphene, aligning with theoretical predictions, and introduces a sensitive measurement technique for exploring Berry phase effects in 2D materials.

Contribution

First direct measurement of graphene's divergent orbital diamagnetism at the Dirac point using a highly sensitive GMR sensor.

Findings

Observed a diamagnetic peak at the Dirac point

Magnetic field and temperature dependence match theoretical models

Demonstrated a new method to probe Berry phase singularities

Abstract

The electronic properties of graphene have been intensively investigated over the last decade, and signatures of the remarkable features of its linear Dirac spectrum have been displayed using transport and spectroscopy experiments. In contrast, the orbital magnetism of graphene, which is one of the most fundamental signature of the characteristic Berry phase of graphene's electronic wave functions, has not yet been measured in a single flake. In particular, the striking prediction of a divergent diamagnetic response at zero doping calls for an experimental test. Using a highly sensitive Giant Magnetoresistance sensor (GMR) we have measured the gate voltage-dependent magnetization of a single graphene monolayer encapsulated between boron nitride crystals. The signal exhibits a diamagnetic peak at the Dirac point whose magnetic field and temperature dependences agree with theoretical predictions starting from the work of Mc Clure \cite{McClure1956}. Our measurements open a new field of investigation of orbital currents in graphene and 2D topological materials, offering a new means to monitor Berry phase singularities and explore correlated states generated by combined effects of Coulomb interactions, strain or moir\'e potentials.