Probing the extended-state width of disorder-broadened Landau levels in epitaxial graphene

We experimentally investigate the width of extended states in disorder-broadened Landau levels (LLs) in top-gated epitaxial graphene on silicon carbide using two different methods: gated transport spectroscopy and activation gap measurements on integer quantum Hall states. The transport spectroscopy reveals that the widths of the extended states in the zero-energy (N = 0) and first excited (N = 1) LLs are of similar magnitude over the ranges of magnetic field (4-16 T) and temperature studied (1.6-150 K). Under certain assumptions we find that the extended-state width follows a power-law temperature dependence with the exponent eta similar to 0.3 in the N = 0 (N = 1) LL, with almost no (very weak) magnetic-field dependence. Activation gap measurements at the filling factors of nu = 2 and 6 give results consistent with transport spectroscopy for the N = 1 LL, but indicate a larger broadening for the N = 0 LL than deduced from the spectroscopy.