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HL: Fachverband Halbleiterphysik
HL 32: C/diamond
HL 32.4: Vortrag
Mittwoch, 28. März 2007, 17:15–17:30, H14
Metal-insulator transition and superconductivity in heavily boron-doped single crystal diamond — •Philipp Achatz1,2,3, Etienne Bustarret1, and Thierry Klein1 — 1CNRS Grenoble/LEPES, 25 Avenue des Martyrs, 38042 Grenoble, France — 2CEA Grenoble/DRFMC/SPSMS, 17 Avenue des Martyrs, 38054 Grenoble, France — 3Walter Schottky Institut, TU München, Am Coulombwall 3, 85748 Garching, Germany
The superconducting properties of diamond epilayers grown along { 001 } and doped with boron (0.3 < nB < 3 at. %) have been investigated at low temperatures down to about 50 mK by a.c. and d.c. resistivity, as well as by a.c. magnetic susceptibility, and the phase diagram of this type II superconductor was established. Further, the results show that the critical boron concentration nc is the same for the normal to superconducting and for the non-metal to metal transitions, on the order of 0.3 at. %, in agreement with estimates derived from various theoretical approaches. A variable range hopping behaviour was clearly observed on the insulating side of the transition, and, as expected, the characteristic temperature T0 tended toward zero at the transition. On the metallic side, the zero temperature conductivity σ0 scaled with (nB/nc − 1)ν with ν ≈ 1. The critical temperature Tc remained high in the vicinity of the metal-non metal transition, and it was rather found to scale with (nB/nc − 1)1/2. These results led us to propose that the electron-phonon coupling parameter λ remains large down to nB/nc ≈ 1.1, and to examine the metal-insulator transition and the parameter set (λ, µ) in terms of scaling laws.