Resonant tunnelling spectroscopy of the local density of states in a disordered conductor

Abstract

We have studied the effects of magnetic field on the fluctuations of the electron density of states in a disordered conductor, a contact in the resonant tunnelling structure GaA1As/GaAs/GaA1As. The local density of states (LDOS) in the contact is detected by an impurity which acts as a 'spectrometer'. In the regime of weak magnetic field, ωcτ ≤ 1, a linear increase of the fluctuation magnitude with B2 is seen, due to the decrease of the volume where the LDOS is formed and a decrease in the statistical averaging. In the regime ωcτ ≥ 1, large oscillations of the fluctuation magnitude have been observed. We suggest an explanation of this new effect, de Haas-van Alphen type oscillations in the fluctuation magnitude. The behaviour of impurity spectrometers in a magnetic field and images given by a complex spectrometer are also discussed.