IQIM Postdoctoral and Graduate Student Seminar

Friday October 17, 2014 4:30 PM

Building new edge states in twisted bilayer graphene: quantum spin Hall state and electron-hole bilayers

Speaker: Javier Sanchez-Yamagishi, Physics, MIT
Location: East Bridge 114

Abstract:

Twisted bilayer graphene is the ultimate thin limit of a bilayer 2DEG, where two graphene layers are stacked with an interlayer distance of only 0.34nm. The interlayer tunnel coupling can be continuously tuned by twisting the two layers, leading to dramatically different physics in the small and large twist angle limits. At large twist angles, interlayer tunneling is suppressed, allowing for the creation of novel edge state configurations based on the graphene quantum Hall effect.  I will discuss our attempts to realize a quantum spin Hall state in twisted bilayer graphene by doping to form an electron-hole bilayer at moderate magnetic fields.  In this regime, counter-propagating edge modes exist on each layer, and the occupation of edge modes on each layer can be independently controlled.  At higher magnetic fields, electron-electron interactions fully break the graphene spin-valley symmetries, and fractional quantum Hall states arise.  I will present our magnetotransport measurements of high-quality twisted bilayer graphene, and discuss how, by independently controlling the filling factor in each layer, we can realize novel states such as twisted bilayer quantum spin Hall states and electron-hole bilayer fractional quantum Hall states.

 

 - Refreshments following the seminar on the Bridge patio.

Series IQIM Postdoctoral and Graduate Student Seminar Series

Contact: Marcia Brown at 626-395-4013 marciab@caltech.edu