Transport measurement of Landau level gaps in bilayer graphene with layer polarization control.

Landau level (LL) 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 factors v = +/- 4 and -2. The single-particle A scales linearly with magnetic field B and is independent of the out-of-plane electric field E-perpendicular to. For the symmetry-broken v = -2 state, the measured values of Delta(v=-2), are similar to 1.1 meV/T and 0.17 meV/T for singly gated geometry and dual-gated geometry at E-perpendicular to = 0, respectively. The difference between the two values arises from the E-perpendicular to dependence of Delta(v=-2), suggesting that the v = -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-perpendicular to and establish a robust method that can be implemented for studying similar states in other layered materials.