Probing Topological Valley Physics in Bilayer Graphene - Long Ju, Cornell University

Tue, Feb 7, 2017, 1:30 pm
Jadwin 303

Graphene has been a model solid state system where novel quantum phenomena emerge from the interplay between symmetry, band topology and reduced dimensionality. In particular, AB-stacked bilayer graphene has a unique bandstructure with an electrically tunable bandgap and a valley-dependent Berry phase. These features result in unusual electrical and optical properties, for which optical spectroscopy/microscopy are powerful characterization tools. In this talk, I will first show our experimental demonstration of the topological valley transport at AB/BA domain walls in bilayer graphene[1]. By combining near field infrared nanoscopy with low temperature electron transport, we showed that a 1D conducting channel exists at this structural domain wall, which can be attributed to the quantum valley Hall edge states in gapped bilayer graphene. Moreover, I will present our recent efforts in probing the exciton physics in bandgap-tuned bilayer graphene through novel optical spectroscopy tools[2]. I will show that due to the valley dependent electron pseudospin winding number and Berry curvature effects, these excitons obey distinct optical selection rules from that in conventional semiconductors and feature a large valley g-factor in magnetic field. 
[1] L. Ju et al. Nature. 520, 650–655 (2015)
[2] L. Ju et al. Unpublished.