Valley landau level crossings in weakly coupled bilayer WSe2

Abstract

Abstract WSe2 is a p-type 2D-semiconductor that can be mechanically exfoliated down to atomic layers. Unlike the Bernal stacked bilayer graphene, the two layers in a bilayer WSe2 flake are weakly coupled. The electric displacement field can easily break the layer degeneracy of the bilayer WSe2. Together with the strong spin–orbit coupling, it exhibits many novel quantum physical properties. In this work, we fabricate high quality dual-gated bilayer WSe2 devices and observe twofold degenerate Landau levels(LLs) and density-dependent quantum Hall states which show transitions between even and odd filling. When introducing carriers into the system from the valence band edge by gating, two WSe2 layers are filled independently and the bottom layer WSe2 shows negative compressibility at the crossover point. Above 9 T, we observe the degeneracy of LLs is completely broken and there are two sets of LL crossings in the top WSe2 layer at Zeeman-to-cyclotron energy ratio E Z / E N ≈ 4 and E Z / E N ≈ 5. The interplay between two LLs from the two WSe2 layers confirms the weak coupling between them. Our results show that the bilayer WSe2 behave like two closely packed independent electronic systems under electric displacement fields.