Transport Measurement of Landau level Gaps in Bilayer Graphene

Abstract

Landau level gaps are important parameters for understanding electronic interactions and symmetry-broken processes in bilayer graphene (BLG). Here we present transport spectroscopy measurements of LL gaps in double-gated suspended BLG with high mobilities in the quantum Hall regime. By using bias as a spectroscopic tool, we measure the gap {\Delta} for the quantum Hall (QH) state at filling factor {\nu}={\pm}4 and -2. The single-particle gap for {\nu}=4 scales linearly with magnetic field B and is independent of the out-of-plane electric field E. For the symmetry-broken {\nu}=-2 state, the measured values of gap are 1.1 meV/T and 0.17 meV/T for singly-gated geometry and dual-gated geometry at E=0, respectively. The difference between the two values arises from the E-dependence of the gap, suggesting that the {\nu}=-2 state is layer polarized. Our studies provide the first measurements of the gaps of the broken symmetry QH states in BLG with well-controlled E, and establish a robust method that can be implemented for studying similar states in other layered materials.