laboratoire pierre aigrain
électronique et photonique quantiques
laboratoire pierre aigrain

Séminaire, 6 Décembre 2013, horaire exceptionnel 15:30

X. R. WANG (Physics Department, The Hong Kong University of Science and Technology, China)
Topological transition of graphene from quantum Hall metal to quantum Hall insulator

In this talk, I will first review the basic electronic properties of graphene. In particular, I will explain why experimentally observed insulating phase of graphene at charge neutrality point in high magnetic field is a big surprise. Then I will present a simple non-interacting one-particle theory for this intriguing finding. We show that the magnetic field driven Peierls-type lattice distortion (due to the Landau level degeneracy) and random bond fluctuations compete with each other, resulting in a transition from a QH-metal state at relative low field to a QH-insulator state at high enough field at the charge neutrality point. The critical field that separates QH-metal from QH-insulator depends on the bond fluctuation. The picture explains well why the field required for observing the insulating phase is lower for a cleaner sample.