Does a magnetic field suppress the Coulomb gap?

We used electron-tunnelling spectroscopy to investigate the Coulomb correla tion in n - type Germanium. The dopant concentration was smaller than the c ritical concentration for the metal-insulator (Anderson) transition. The tu nnelling conductance, which probes the electronic density of states, was fo und to depend strongly on both voltage and temperature. At low temperatures it shows a conductance minimum at the Fermi energy as expected for the Cou lomb correlation gap. Applying a magnetic field up to B = 4T at T = 0.1 K r educes the magnitude of the tunneling conductance, but does not significant ly change the shape of the spectra. At higher fields, the conductance minim um disappears, suggesting a suppression of the Coulomb gap. This could be d ue to the field-induced confinement of the electron wave functions, that st rongly reduces the overlap between the localized electron states.