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

The electronic properties of graphene have been intensively investigated over the past decade. However, the singular orbital magnetism of undoped graphene, a fundamental signature of the characteristic Berry phase of graphene's electronic wave functions, has been challenging to measure in a single flake. Using a highly sensitive giant magnetoresistance (GMR) sensor, 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 long-standing theoretical predictions. Our measurements offer a means to monitor Berry phase singularities and explore correlated states generated by the combined effects of Coulomb interactions, strain, or moire potentials.