Intersubband Landau Level Couplings Induced by In-Plane Magnetic Fields in Trilayer Graphene.

We observed broken-symmetry quantum Hall effects and level crossings between spin- and valley- resolved Landau levels (LLs) in Bernal stacked trilayer graphene. When the magnetic field was tilted with respect to the sample normal from 0° to 66°, the LL crossings formed at intersections of zeroth and second LLs from monolayer-graphene-like and bilayer-graphene-like subbands, respectively, exhibited a sequence of transitions. The results indicate the LLs from different subbands are coupled by in-plane magnetic fields (B_{∥}), which was explained by developing the tight-binding model Hamiltonian of trilayer graphene under B_{∥}.