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221.
D. Elefant G. Reiss C. Baier 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):45-53
On bulk layered single crystals (Bi0.25Sb0.75)2Te3 with a hole concentration cm-3 and a mobility cm2/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de
Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the
damping of the amplitudes with increasing temperature the cyclotron mass m
c
= 0.12m
0
is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The
weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected
as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection
with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the
bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide
with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier
reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be .
Received: 12 September 1997 / Revised: 8 January 1998 / Accepted: 22 January 1998 相似文献
222.
Daniel M. Baier Carolina Spula Stephen Fanenstich Dr. Sven Grätz Prof. Dr. Lars Borchardt 《Angewandte Chemie (International ed. in English)》2023,62(20):e202218719
Photochemical reactors inherently suffer from the low penetration depth of light and therefore rely on high dilutions to enable chemical reactions. Here we present the first method of UV (ultraviolet) photochemistry in the complete absence of bulk solvents in a ball mill. Triphenylene was synthesized by two routes, the Mallory reaction and the cyclodehydrochlorination (CDHC), resulting in yields of 81 and 92 %, respectively. The reaction was successfully scaled up to the gram scale and the robustness of the method was demonstrated for several different substrates. Finally, the regioselective assembly of nanographenes by mechanochemistry was demonstrated for larger systems. Thus, the mechanochemical approach presented here provides a powerful new tool for the atomically precise construction of nanographenes. 相似文献
223.
H. Baier 《Fortschritte der Physik》1979,27(5):209-260
Some recent attempts to take into account exchange currents and isobaric excitations in the electromagnetic and weak interactions of leptons with the deuteron are reviewed. After a presentation of the relevant theoretical framework the crucial experiments supporting strongly the exchange current ideas are discussed in some detail. 相似文献