Local spectroscopy of Landau levels in mesoscopic Hall bars
Résumé
We performed a local spectroscopy of the Landau levels density of states using gated mesoscopic Hall bars placed at very low temperature in the integer quantum Hall regime. The transverse and longitudinal conductances were measured while scanning both the two-dimensional electron density and the applied magnetic field. We observe a succession of sharp peaks due to backscattering across the samples caused by tunneling effects. Using temperature as a parameter in the range of 0.1-1 K, we characterize those tunnel processes: a resonant double-barrier tunneling and a single-barrier tunneling which corresponds to the variable range hopping regime. We show that for vanishing temperature and noninteger filling factor nu the conductance sigma(T=0, nu) does not vanish unlike the case of wide samples: instead, it converges to a limit function sigma(S)(nu) that is a noisy image of the Landau levels density of states.