On the gap problem for the sequence ∥mβ∥

We discuss the gap problem for the sequence m used in our previous Letter (D. H. Mayer, Lett. Math. Phys. 16, 139–143 (1988)).     

Hot hole effects in uniaxially stressedp-type germanium under E∥P∥ [1 1 1]

High field behaviour of holes in uniaxially stressedp-type germanium for stressP and the electric fieldE along the [1 1 1] axis is studied. The field dependence of the drift velocity, the frequency dependence of the longitudinal differential mobility and the spectral dependence of the sub-band population for direct hole transitions between the upper and lower splitted sub-bands are calculated by the Monte-Carlo method. A Gunn-type negative differential mobility is demonstrated to appear atP 7 to 8 kbar,E 0.15 to 4 kV cm^–1 in a frequency rangev 0 to 100 GHz. It is shown, that the stimulated emission and current increase observed by I. V. Altuhovet al. [1] cannot be ascribed to the direct hole transitions between the sub-bands because the population inversion of the transitions is absent.     

Investigation of the π–π stacking interactions without direct electrostatic effects of substituents: the aromatic∥aromatic and aromatic∥anti-aromatic complexes

Stability of the π–π stacking interactions in the ben∥substituted-ben and ben∥substituted-COT complexes was studied using the computational quantum chemistry methods (where ben and COT are benzene and cyclooctatetraene, ∥ denotes π–π stacking interaction, substituted-ben and substituted-COT are benzene and cyclooctatetraene which substituted with four ethynyl-X groups, respectively, and X = OH, CH₃, H, F, CF₃, CN and NO₂). In these complexes electron-withdrawing substituents lead to larger binding energies and electron-donating ones lead to weaker interactions compared to X = H. There are meaningful correlations between the Hammett constants and binding energies. The atoms in molecules (AIM) analysis shows that formation of these complexes is accompanied by increase in the electron charge densities at the ring critical points of the substituted-ben and substituted-COT rings which leads to increase/decrease of the π–π stacking interactions in the ben∥substituted-ben/ben∥substituted-COT complexes. The charge transfer occurs from benzene to substituted-ben in the ben∥substituted-ben complexes and from substituted-COT to benzene (with the exception of X = CN) in the ben∥substituted-COT ones. Nuclear magnetic resonance calculations demonstrate that interactions of the more aromatic substituted-ben/less anti-aromatic substituted-COT rings with benzene in the ben∥substituted-ben/ben∥substituted-COT complexes can be helpful to enhance strength of the π–π stacking interactions. Thus, regardless of ring size, the π–π stacking interaction is an aromatic–aromatic interaction and π electron cloud properties of interacting rings affect on the strength of this interaction.     

Capacitance-voltage behaviour inp-type ɛ-GaSe single crystal ∥c at different temperatures

Summary  Capacitance-voltage measurements have been carried out onp-type ɛ-GaSe single crystal ∥c in the temperature range 300 to 360 K, with applied voltages of -1, 0 and +1 V. TheC-V measurements in this temperature range have shown a shift in capacitanceC and conductanceG to the higher values with an increase in temperature. The depletion layer widthW, the Debye length L_D and the doping densityN _α have been worked out and plots ofN _α vs. W have shown a decrease inW with an increase in temperature. The plots of L_D vs. N _α vary as 1/N_α^1/2, which gives N_αL_D ⋍ 3.3 × 10¹¹ charges/m² for doping density of 10¹⁶m⁻³. The values ofG at different temperatures have been used to obtain the activation energies, which are found to be ΔE ⋍ 0.11 eV for -1 and +1 V applied voltages, and ΔE ⋍ 0.06 eV for zero volt. The authors of this paper have agreed to not receive the proofs for correction.     

YBa2Cu3O7-δ体系在B∥I∥c下磁场引起的电阻耗散

基于最近提出的平面外电阻耗散模型,计算了YBa_2Cu_3O_(7-8),体系在平行于c轴的磁场下不同温度时的平面外磁阻率ρ-B和不同磁场时的平面外电阻转变ρ-T.该模型预言了文献上普遍报道的该体系在外加磁场下的Lorentz力无关的耗散行为.为确信这一点,作为例子,特别将由该模型预言的理论结果与在YBa_2Cu_5O(7-8)体系中在B//I//c下测得的电阻转变曲线进行了定量地比较. 关键词：