Experimental detection of graphene's singular orbital diamagnetism at the Dirac point.

The electronic properties of Graphene have been intensively investigated over the last decade, and signatures of the remarkable features of its Dirac spectrum have been displayed using transport and spectroscopy experiments. In contrast, the orbital magnetism of graphene, which is probably the most fundamental signature of graphene’s characteristic Berry phase, has not yet been measured at the level of 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 magnetisation of a single graphene flake encapsulated between boron nitride (BN) 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 McClure in 1956 [1]. Our measurements open a new field of investigation of orbital currents in graphene and 2D topological materials, providing a new means of monitoring Berry phase singularities and exploring correlated states generated by combined effects of Coulomb interactions strain or Moiré potentials.

[1] McClure, J. W., Physical Review, 104(3), 666, 1956.