Regensburg 2000 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 22: Postersitzung III: Supraleitende Anwendungen (1-4) Massive HTSL, Bandleiter, Filme (5-26), Transport in HTSL (27-30), Elektronenstruktur in Supraleitern (31-43), Borkarbide (44-50), Quantenphasen- und Metall-Isolator-Überg
änge (51-69)
TT 22.69: Poster
Donnerstag, 30. März 2000, 14:00–17:30, A
Variable-range hopping conductivity in Si:P — •Mahdi Iqbal, Ralf Vollmer, Sibylle Waffenschmidt, and Hilbert v. Löhneysen — Physikalisches Institut und SFB 195, Universität Karlsruhe, D-76128 Karlsruhe
The low-temperature electrical conductivity σ (T) of uncompensated insulating Si:P with P concentration N just below the metal-insulator transition (MIT), i.e., 3.0 ∼< N ∼< 3.5 · 1018cm−3, was measured between 0.05 K and 5 K. With decreasing N, σ (T) shows a crossover from Mott variable-range hopping (VRH) to Efros-Shklovskii VRH. The data on the insulating side can be combined with those on the metallic side of the MIT to yield dynamic scaling of σ(N,T), similar to what has been found for σ(S,T) scaling under uniaxial stress S [1]. Upon lowering N on the insulating side further, a change from Efros-Shklovskii VRH to simple activated conduction is observed near N ≈ 2.7 · 1018cm−3 above 1.6 K. This is attributed to the activation from the lower to the upper Hubbard band, as inferred from a sign change in the thermoelectric power and the absence of such a feature in compensated Si:(P,B). In addition, VRH data in high magnetic fields will be presented.
[1] S. Waffenschmidt et al., Phys. Rev. Lett. 83, 3005 (1999)