Impact of Parallel Computing on Study of Time Evolution of a Quantum Impurity System in Response to a Quench

In an arbitrary system subjected to a quench, or an external field that varies the system parameters, the degrees of freedom increases double in comparison to that of an isolated system. In this study, we consider the quantum impurity system subjected to a quench, and measure the corresponding time-evolution of the spectral function, which is originated from the time-resolved photoemission spectroscopy. Due to the large number of degrees of freedom, the expression of the time-dependent spectral function is twice much more complicated than that of the time-independent spectral function, and therefore the calculation is extremely time consuming. In this paper, we estimate the scale of time consumption of such calculation in comparison to that of time-independent calculation, and present our solution to the problem by using parallel computing as implementing both MPI and OpenMP to the calculation. We also discuss the possibility to exploit parallel computing with GPU in the near future, and the preliminary results of time-dependent spectral function.

Peculiarities of Electrical Characteristics of Semi-Insulating CdTe-Сl crystals

Electrical properties of semi-insulating CdTe-Сl crystals, grown by the vertical Bridgman and the travelling heater method, have been studied. It is found that the travelling heater method provides electron conductivity of the crystals, and the vertical Bridgman method – hole conductivity. Specific resistance of the samples is of (108-109) Ohm×сm at 300 K, and Hall mobility of the holes and electrons is of (45 - 55) cm2/V·s and (10 - 20) cm2/V·s respectively. Very low values of electron mobility and an exponential temperature dependence of µn are due to drift barriers with a height of εb ≈ 0.20 eV. Formation of the barriers is caused by the fluctuations of the potential relief resulting from the microheterogeneity of the defect-impurity system. Quasi-photochemical reactions that reduce electron mobility after photo-excitation have been observed in n-CdTe-Cl samples. In p-CdTe-Cl samples, neither drift barriers, nor quasi-photochemical reactions were detected.

Nonlinear entangled quantum dynamics in many-body systems with strong electron correlation

A quantum impurity system out of equilibrium comprises two metallic reservoirs with different chemical potentials and one mediating spin impurity between them. We study the highly nonlinear tunneling conductance of this system, and clarify that three coherent peaks, one zero-bias peak and two side peaks, naturally appear in the tunneling conductance. We use the Liouvillian approach, in which a complete set of basis operators is available, and construct a Liouville matrix to obtain Green’s function at the mediating site. We show that the two coherent side peaks are the outcome of steady-state nonequilibrium combined with strong electron correlation at the mediating site. Tunneling in the quantum impurity system out of equilibrium is performed by an entangled state which is a linear combination of two Kondo singlets formed by the spin at the mediating site and the coherent spins in each reservoir. The fluctuation by incoherent spins is also included. The spectral weights and positions of the three coherent peaks are analytically discussed via atomic limit analysis. Our theoretical results well fit experimental data obtained for quantum point contacts with symmetric and asymmetric Kondo couplings.

Miniband Electroconductivity in Superlattices of Cubic Quantum Dots of the InAs/GaxIn1-xAs Heterosystem

In this paper, the model of InAs/GaxIn1-xAs cubic quantum dot superlattices (CQDS) of various dimensionality has been proposed. The energy spectra of electrons and holes of the quantum dot superlattice have been determined in the effective mass approximation and modified Kronig-Penney model. In the frame of this model, the spectra of charges of 3D, 2D and 1D-superlattices can be obtained by changing respective distances between the elements of the superlattice. The energy dependence of the electron and hole subbands (under-the-barrier subbands and over-the-barrier subbands) on the wave vector of the superlattice has been calculated. The number of under-the-barrier subbands is determined by QD size and width of each subband is defined by QD size, distances between superlattice elements and subband numerical index. The dependences of the Fermi energy and concentration of charge carriers on temperature, concentration of impurities, energy of impurity levels have been obtained and analyzed. We have taken account of the dependence of electron relaxation time on temperature caused by scattering of carriers on both phonons and donor centers. The effect of the impurity system on electroconductivity of the CQDS is investigated.

Review of the Application of Water Pinch Technology in Water-Saving and Emission Reduction

Water pinch technology for the water system of enterprises is one of the focuses on water-saving and emission reduction research of enterprises in recent years. This technology is characterized by the design minimal fresh water consumption and waste water emissions minimum and aims to achieve economic benefit optimum process integration technology. The application of water pinch technology to integration and optimization of the water system was reviewed, and engineering application examples of water pinch technology were introduced. The water pinch technology is simple and intuitive. Besides, it could achieve optimal solution for a single impurity system. But for multiple contaminants system, this method will no longer apply. Taking into account its limitations, the possible optimization solutions to application of water pinch technology in combination with other types of analysis tools in enterprise water system were put forward.