Condensed Matter Seminar: "The Case for an Exciton Metal in Bilayer Graphene"

Wed, 10/04/2017 - 16:00 - 17:00
Michael Zaletel (Princeton University)

Graphene based heterostructures have emerged as a pristine platform for exploring the interplay of symmetry, topology and non-Abelian excitations in the quantum Hall regime. I will begin with a theoretical review of the quantum Hall effect in bilayer graphene before discussing results in collaboration with the Young Lab at UCSB. Using in-situ control of the density and electro-magnetic fields, they find a rich phase diagram which features a plateau at half-filling of a Landau level with a gap several times larger than previously observed. Comparison between experiment, theory and numerical work suggests this is the Moore-Read Pfaffian phase with emergent Majorana fermions. When an electric field is applied, they observe a quantum phase transition between the gapped Pfaffian phase and a gapless composite Fermi liquid. I will propose this transition is mediated by the formation a Fermi sea of neutral excitons, which would provide new evidence for fractionalization.

David Rittenhouse Laboratory, A4