The key role of smooth impurity potential in formation of hole spectrum for p-Ge/Ge_{1-x}Si_x heterostructures in the quantum Hall regime

We have measured the temperature (0.1 <= T <= 15 K) and magnetic field (0 <= B <= 12 T) dependences of longitudinal and Hall resistivities for the p-Ge_0.93Si_0.07/Ge multilayers with different Ge layer widths 10 <= d_w <= 38 nm and hole densities p_s = (1-5)10^11 cm^-2. Two models for the long-range random impurity potential (the model with randomly distributed charged centers located outside the conducting layer and the model of the system with a spacer) are used for evaluation of the impurity potential fluctuation characteristics: the random potential amplitude, nonlinear screening length in vicinity of integer filling factors nu = 1 and nu = 2 and the background density of state (DOS). The described models are suitable for explanation of the unusually high value of DOS at nu = 1 and nu = 2, in contrast to the short-range impurity potential models. For half-integer filling factors the linear temperature dependence of the effective QHE plateau-to-plateau transition width nu_0(T) is observed in contrast to scaling behavior for systems with short-range disorder. The finite T -> 0 width of QHE transitions may be due to an effective low temperature screening of smooth random potential owing to Coulomb repulsion of electrons.Comment: Accepted for publication in Nanotechnolog

Effect of exchange electron-electron interaction on conductivity of InGaAs single and double quantum wells in ballistic regime

We report an experimental study of quantum conductivity corrections for two-dimensional electron gas in a GaAs/InGaAs/GaAs single and double quantum wells in a wide temperature range (1.8-100) K. We perform a comparison of our experimental data for the longitudinal conductivity at zero magnetic field to the theory of interaction-induced corrections to th transport coefficients. In the temperature range from 10 K up to (45-60) K, wich covers the ballistic interaction regimes for our samples, a rather good agreement between the theory and our experimental results has been found

Parabolic negative magnetoresistance in p-Ge/Ge1-xSix heterostructures

Quantum corrections to the conductivity due to the weak localization (WL) and the disorder-modified electron-electron interaction (EEI) are investigated for the high-mobility multilayer p-Ge/Ge1-xSix heterostructures at T = (0.1 - 20.0)K in magnetic field B up to 1.5T. Negative magnetoresistance with logarithmic dependence on T and linear in B^2 is observed for B >= 0.1T. Such a behavior is attributed to the interplay of the classical cyclotron motion and the EEI effect. The Hartree part of the interaction constant is estimated (F_/sigma = 0.44) and the WL and EEI contributions to the total quantum correction /Delta /sigma at B = 0 are separated (/Delta /sigma_{WL} ~ 0.3/Delta /sigma; /Delta /sigma_{EEI} ~ 0.7/Delta /sigma).Comment: 3 pages, 4 figure

Метод генерации сочетаний для параллельных вычислений

В предыдущих работах решалась задача составления оптимального производственного расписания. Для оптимизации процесса потребовался метод генерации сочетаний, пригодный для использования на графических процессорах. Обзор литературы показал, что предлагаемые решения не оптимальны, поэтому было решено разработать такой метод самостоятельно. В основе разработанного метода лежит другой принцип представления комбинаторных объектов. Благодаря этому номера объектов, составляющих выборку, можно вычислять алгебраически, без использования циклов и операций ветвления.In previous works we solved the problem of optimal production schedules. To optimize the process, a method of generating combinations, suitable for use on graphics processing units, was needed. Literature review showed that the proposed solutions are not optimal, so it was decided to develop a method of their own. The basis of this method is another principle of representation of combinatorial objects. This allows computing algebraically sample’s objects numbers, without using loops and branching operations