Condensed Matter Seminar | Cory Dean, Columbia, "Correlated states in bilayer graphene in the quantum Hall regime" | PCTS Seminar Room 407

Mon, Nov 6, 2017, 1:15 pm
PCTS Seminar Room 407


Soon after the discovery of monolayer graphene, it was shown that bilayer graphene (BLG), consisting of two bernal stacked monolayers,  could theoretically support an even-denominator fractional quantum Hall state equivalent to the 5/2 Moore-Read Pfaffian first identified in GaAs . Owing to the unique landau level spectrum in BLG, the Pfaffian in this system is expected to be tunable by electric and magnetic fields, with the potential to be stronger than in GaAs for accessible field parameters. In my talk I will discuss recent magnetotransport studies of high mobility, BLG. Utilizing a dual gate geometry to tune through different orbital and layer polarizations, we find four even denominator states appearing within the N = 1 orbital branches of the lowest LL. We investigate how these states evolve with varying parameters and provide the first mapping of the B – D phase diagram. Our results confirm the unique tunability of the even denominator state in BLG, and we reach a regime where the energy gap is found to exceed several kelvin.  I will also present recent measurements of bilayer systems in which we separate the two layers by a thin BN spacer.  Here, by tuning the interlayer interaction strength via the layer separation, we are able to stabilize new correlated states in the double layer systems formed from interlayer excitons.