Direct observation of the electron spectral function in the integer and fractional quantum Hall regimes by resonant tunneling

Low-temperature current-voltage characteristics of a double-barrier resonant tunnel junction are used to directly measure the two-dimensional (2D) electron spectral function. Our data provide quantitative determination of the 2D density of states, including chemical potential and linewidth oscillations as a function of magnetic field up to 51 T. We also measure a chemical potential jump at 1/3 fractional filling of the lowest Landau level.