Observation of Symmetry Breaking in High Mobility Graphene

MasterSince graphene was discovered in 2004, this novel material has recently received considerable attention from many areas. Because graphene has the linear energy–momentum dispersion relation, it makes high energy physics correlated to condensed matter physics. One of the most remarkable accomplishment of solid state physics in 1980s is quantum Hall effect. Quantum Hall effect is described by quantization of conductance in units of e^2/h. It has standard resistance regardless of matter. In graphene with degeneracy per Landau level g=4, N=0 Landau level has electron regime half-filled and the other half regime has hole carrier. This behavior is particularly different from other two-dimensional electron systems. Thus graphene has Hall conductance, which increases in units of ±〖4e〗^2/h for electron/hole carriers. Symmetry breaking was observed from quantum Hall effect in graphene. Filling factor ±1, ±4 arises as the spin degeneracy is lifted and 0 attributes to the sublattice degeneracy. In 2013, h-BN(Hexagonal-Boron Nitride)/graphene/h-BN encapsulated technique was developed in association with one-atom-thick edge contact. This remarkable technique can be used to highly increase mobility. In high-mobility graphene, symmetry breaking is expected that observed in lower magnetic field comparable to raw graphene in quantum Hall effect measurements. It agrees with our research data in that valley degeneracy is lifted observed even in 3T and spin degeneracy completely lifted in 8T. From gate vs Hall conductace graph, we observeν=0,±1,±2,±3,±4,±5,±6, 7quantum Hall plateaus. In bias spectroscopy experiment, we observed Landau level energy gaps in quantum Hall regime. It was strange to observe filling factor 2 Landau level gap size very large comparable to others quantum Hall regime. So far, Landau level gaps in quantum Hall regime of graphene have rarely been examined. Thus measurements of landau level gaps in quantum Hall regime of graphene are highly meaningful. Consequently, we investigated quantum Hall effect in high mobility graphene using h-BN/graphene/h-BN encapsulated techinique and symmetry breaking was observed represented by filling factors 0, ±1, ±4