Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 4: Matter at Low Temperature: Materials
TT 4.6: Vortrag
Montag, 25. Februar 2008, 11:00–11:15, H 3010
Effect of the Magnetic Field on the Coulomb Gap — •Barbara Sandow1, Dirk Brossell1, Olaf Bleibaum2, and Walter Schirmacher3 — 1Institut für Experimentalphysik, Freie Universität Berlin, Germany — 2Institut für Theoretische Physik, Otto-von-Guericke Universität Magdeburg, Germany — 3Physik-Department E13, Technische Universität München, Germany
We used break-junction tunnelling spectroscopy to investigate the Coulomb correlation in n-type Germanium. The doping concentration was smaller than the critical concentration for the metal-insulator (Anderson) transition. The tunnelling conductance, which probes the electronic density of states, was found to depend strongly on voltage, temperature and magnetic field.
At low temperatures the differential conductance shows a minimum at zero voltage, as expected for a material with a Coulomb gap near the Fermi energy. Applying a magnetic field up to B = 8 Tesla at T = 0.1 K to 1 K reduces the magnitude of the tunnelling conductance. Furthermore our data on n-type Germanium seem to indicate a strong suppression of the Coulomb gap in large fields. This could be due to the field-induced shrinking of the electron wave functions that strongly reduces the overlap between the localized electron states. Using our theory of break-junction tunnelling in the hopping regime [1] we are able to explain the disappearance of the Coulomb gap in high magnetic fields.
[1] O. Bleibaum, B. Sandow, W. Schirmacher, Phys. Rev. B 70, 045308-1 (2004)