Topic: Excitonic superfluid phase in double bilayer graphene
       石墨烯中基于库伦拖拽的激子超流现象

Speaker: J.I.A. Li  (李嘉)
             Physics Department at Columbia University, New York.

Time: 15:00-16:30, (Mon.) May 15^th, 2017

Venue: Room 403，Shi Changxu Building, IMR CAS

Abstract

A spatially indirect exciton is created when an electron and a hole, confined to separate layers of a double quantum well system, bind to form a composite Boson. Such excitons are long lived, and in the limit of strong interactions are predicted to undergo a BEC-like phase transition into a superfluid ground state. We will discuss here evidence of the exciton condensate in the quantum Hall effect regime of double layer structures of bilayer graphene. Interlayer correlation is identified by quantized Hall drag at matched layer densities, and the dissipationless nature of the phase is confirmed in the counterflow geometry. A selection rule for the condensate phase is observed involving both the orbital and valley indices of bilayer graphene. Our results establish double bilayer graphene as an ideal system in which to study the rich phase diagram of strongly interacting Bosonic particles in the solid state [1-2].

[1] JIA Li, et al., Nature Physics, accepted, 2017.
[2] JIA Li, et al., Phys. Rev. Lett. 117, 046802, 2016.

Brief bio

Dr. J.I.A. Li is currently a post-doc researcher at Columbia University, in the nano-electronic lab under Prof. Cory Dean. He got his Ph.D from Northwestern University studying order parameter structure of novel 3He superfluid phases using pulsed NMR method. His current research focuses on multi-component emergent phases in graphene-hexagonal Boron-Nitride based heterostructures, e.g., exciton condensate state in double bilayer graphene.