Resonant Tunnelling Spectroscopy of the Local Density of States in a Disordered Conductor

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 GaAlAs/GaAs/GaAlAs. 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.