Quantum motion with trajectories: beyond the Gaussian beam approximation

A quantum model based on a Euler-Lagrange variational approach is proposed. In analogy with the classical transport, our approach maintain the description of the particle motion in terms of trajectories in a configuration space. Our method is designed to describe correction to the motion of nearly localized particles due to quantum phenomena. We focus on the simulation of the motion of light nuclei in ab initio calculations. Similarly to the Gaussian beam method, our approach is based on a ansatz for the particle wave function. We discuss the completeness of our ansatz and the connection of our results with the Bohm trajectories approach

Stochastic model for quantum spin dynamics in magnetic nanostructures

We develop a numerical model that reproduces the thermal equilibrium and the spin transfer mechanisms in magnetic nanomaterials. We analyze the coherent two-particle spin exchange interaction and the electron-electron collisions. Our study is based on a quantum atomistic approach and the particle dynamics is performed by using a Monte Carlo technique. The coherent quantum evolution of the atoms is interrupted by instantaneous collisions with itinerant electrons. The collision processes are associated to the quantum collapse of the local atomic wave function. We show that particle-particle interactions beyond the molecular field approximation can be included in this framework. Our model is able to reproduce the thermal equilibrium and strongly out-of-equilibrium phenomena such as the ultrafast dynamics of the magnetization in nanomatrials

Wigner model for quantum transport in graphene

The single graphene layer is a novel material consisting of a flat monolayer of carbon atoms packed in a two-dimensional honeycomb-lattice, in which the electron dynamics is governed by the Dirac equation. A pseudo-spin phase-space approach based on the Wigner-Weyl formalism is used to describe the transport of electrons in graphene including quantum effects. Our full-quantum mechanical representation of the particles reveals itself to be particularly close to the classical description of the particle motion. We analyze the Klein tunneling and the correction to the total current in graphene induced by this phenomenon. The equations of motion are analytically investigated and some numerical tests are presented. The temporal evolution of the electron-hole pairs in the presence of an external electric field and a rigid potential step is investigated. The connection of our formalism with the Barry-phase approach is also discussed

Bose-Einstein condensation of positronium: modification of the s-wave scattering length below the critical temperature

The production of a Bose-Einstein condensate made of positronium may be feasible in the near future. Below the condensation temperature, the positronium collision process is modified by the presence of the condensate. This makes the theoretical description of the positronium kinetics at low temperature challenging. Based on the quasi-particle Bogoliubov theory, we describe the many-body particle-particle collision in a simple manner. We find that, in a good approximation, the full positronium-positronium interaction can be described by an effective scattering length. Our results are general and apply to different species of bosons. The correction to the bare scattering length is expressed in terms of a single dimensionless parameter that completely characterizes the condensate

Ultrafast Magnetization Dynamics in Diluted Magnetic Semiconductors

We present a dynamical model that successfully explains the observed time evolution of the magnetization in diluted magnetic semiconductor quantum wells after weak laser excitation. Based on the pseudo-fermion formalism and a second order many-particle expansion of the exact p-d exchange interaction, our approach goes beyond the usual mean-field approximation. It includes both the sub-picosecond demagnetization dynamics and the slower relaxation processes which restore the initial ferromagnetic order in a nanosecond time scale. In agreement with experimental results, our numerical simulations show that, depending on the value of the initial lattice temperature, a subsequent enhancement of the total magnetization may be observed within a time scale of few hundreds of picoseconds.Comment: Submitted to PR

Mathematical analysis of a nonparabolic two-band Schrödinger-Poisson problem

Abstract A mathematical model for the quantum transport of a two-band semiconductors that includes the self-consistent electrostatic potential is analyzed. Corrections beyond the usual effective mass approximation are considered. Transparent boundary conditions are derived for the multi-band envelope Schrödinger model. The existence of solution of the nonlinear system is proved by using an asymptotic procedure. Some numerical examples are included. They illustrate the behavior of the scattering and the resonant states

Different Approaches for Multiband Transport in Semiconductors

We compare the well-known Kane model with a new multiband envelope function model, which presents many advantages with respect to the first one.Добре відому модель Кане порівняно з новою моделлю багатокомпонентної обвідної функції i продемонстровано багато переваг останньої

Acute hemolysis by hydroxycloroquine was observed in G6PD-deficient patient with severe COVD-19 related lung injury.

Our patient might be affected by Mediterannean variant of G6PD deficiency, which is more sensitive to pro-oxidant drugs compared to African G6PD A variant. No conclusive data are available on the possible pro-hemolytic impact of CQ/HCQ on patient with G6PD deficiency [3\u20135]. In COVID-19 emergency we believe it is important to warning the possible hemolytic effects of CQ/HCQ in patients with G6PD deficiency. Thus, the acute drop in Hb levels in the early days of CQ/HCQ treatment of COVID19 symptomatic patient should be considere