Mechanism of energy relaxation in the system of Landau levels in quantum wells

The kinetics of intersubband relaxation of electron energy has been studied in the system of Landau levels lying below the optical phonon energy. The relaxation character in the considered system is revealed to differ qualitatively from that in the two-dimensional continuous subband of the quantum well. In particular, the mechanisms of electron subsystem thermalization and energy relaxation in the system of Landau levels are qualitatively different, and the electron subsystem relaxation time exceeds the thermalization time by several orders of magnitude.     

Multistability of states of a molecular gas with the V-T relaxation time dependent on the vibrational energy

The possibility of realizing multistability of states under the action of IR radiation on a molecule under conditions of nonlinear absorption of light energy and dependence of the V-T relaxation time on its vibrational energy is shown. A two-wave optically bistable arrangement potentially having a highly contrasting range of states is proposed. The nonlinear dependence of the V-T relaxation time on the vibrational energy is shown to allow the realization of optical bistability based on the absorption of light energy at the frequency of the fundamental vibrational transition.     

Estimating the energy performance of an insulator with regard to the relaxation time distribution

The energy relationships in the macroscopic electrodynamics of an insulator are analyzed with regard to the polarization relaxation time distribution. Expressions for the discharge power and discharge energy flux densities in an insulator are derived for an electric field exponentially depending on time. The performance of polyethylene terephthalate in capacitive energy storage systems is estimated in terms of energy.     

On the spin-flip line shape in CdS

The longitudinal relaxation time of Spin-Flip Raman scattering (SFRS) in n-CdS is explained in terms of the Elliott mechanism. The energy dispersion of spectroscopic factors of the conduction electrons and the Hasegawa model yield a transversal relaxation time different from the longitudinal relaxation time, but do not reproduce the experimental value. The diffusion coefficient, responsible for the SFRS line width behavior with temperature in n-CdS, is explained based upon hopping effects in the low temperature region.     

Relaxation of the Electron Distribution Function

This paper discusses an analytical technique for calculating the relaxation in time of the electron distribution function f in an environment in which no perturbing forces act on the electrons. For t = 0, f may have any arbitrary form presumed to be caused by perturbing forces which were not zero during t < 0. The technique then allows calculation of the relaxation of f in time for the following types of electron collisions: a) elastic collisions with cold neutrons, b) excitation collisions in which the threshold energy for an elastic excitation collision is small compared to the electron energy, c) ionizing collisions when the energy lost by the electron is small compared to its energy, and d) any combination of the above. In this paper the method is described and simple examples are presented to illustrate the physics of relaxation for the collisional categories listed above. It is pointed out that a number of important problems can be solved by this technique primarily in the area of nuclear EMP: the forrnative lag time problem and the calculation of thermalization time. In addition, the details of the afterglow of extinguished discharges in the monotomic gases can be determined.     

Magnetoresistance effect obtained from the band structure of a crystalline solid

This paper demonstrates that the Lorentz equation combined with the equation for electron drift in an external magnetic field gives a definite value for the relaxation time of the electron motion in a crystalline solid in the aforementioned field. The main result is that the product of the relaxation time and the strength of the magnetic field remain constant and are dependent only on the structure of the energy band of the solid. Free electrons, or nearly free electrons, result in the diagonal components of the tensor for magnetoresistance tending to zero for all electron states. For the electrons in a crystal lattice, the relaxation time considered along the cross-section line in the reciprocal space of a plane normal to the magnetic field and the surface of constant energy become highly anisotropic quantities.     

Simulation of transport and relaxation of hot electrons in the near-surface layers of nanostructured and crystalline silicon dioxides

Computer simulation has been performed to investigate the transport and energy relaxation of photoelectrons in the near-surface layers of nanostructured and crystalline silicon dioxides in the presence and absence of an electric field. Calculations have shown that nanostructured samples have a shorter hot-electron thermalization time and exhibit weaker influence of an electric field on the electron energy relaxation process than the bulk crystal. The size effect calculated in terms of electron thermalization time is most pronounced at particle sizes less than 5 nm.     

Nonequilibrium states of the soft mode anharmonic phonons

A theory of the nonequilibrium state of the soft mode optical phonons in ferroelectrics exposed to the pumping electromagnetic field has been developed. The self-consistent field equation, which determines the phase transition temperature shift and the dielectric permeability change due to a deviation of the system from the equilibrium state is derived. A two-temperature model describing the energy transport in the presence of pumping is suggested. Analytic solutions of this model both for evolving in time and for stationary states are obtained. Spatial oscillations of the soft mode temperature are predicted for the observation time approximately equal to the energy relaxation time. It is shown that nonlinear effects can be a reason of forming of the bottleneck in the energy relaxation process. An exactly solvable model of a breather: the breather with the one-site non-linearity has been constructed and investigated.     

Ab initio GW calculations of the time and length of spin relaxation of excited electrons in metals with inclusion of the spin-orbit coupling

An ab initio method has been proposed for calculating the spin relaxation time of excited electrons in metals in the framework of the GW method with inclusion of the spin-orbit coupling. The time and length of spin relaxation in Al, Cu, Au, Nb, and Ta have been calculated. The concept of the spin-flip phase space has been introduced. It has been demonstrated that the ratio between the spin relaxation time and the lifetime of the excited electron is well explained within this concept. The time and length of spin relaxation in Nb appear to be considerably shorter than those in Al, Cu, and Au. These quantities in Ta are especially small in accordance with the strong spin-orbit coupling. A comparison of the results with the previous data on the time and length of spin relaxation due to the interaction with impurities and phonons shows that, at an excited electron energy of the order of 1 eV, the inelastic electron-electron scattering in the presence of spin-orbit coupling is a dominant mechanism of spin relaxation.     

On the annealing of junction disclinations in deformed polycrystals

The kinetics of relaxation of disclination quadrupoles formed within triple junctions of grains during plastic deformation are studied. The calculations are made using the discrete dislocation model for disclinations by simulating the climb of dislocations. Exponential relationships are obtained for the relaxation of the strength and elastic energy of disclination quadrupoles with a characteristic time proportional to the cube of grain size. The distribution of vacancy fluxes along grain boundaries (GBs) during the relaxation of a disclination quadrupole is studied in detail. The relation between continuum and discrete dislocation approaches to a study of the GB recovery process is considered. Characteristics of each relaxation stage are studied. A hierarchy of characteristic relaxation times for dimerent grain size ranges is constructed and it is show that in nanocrystalline materials the spreading time of trapped lattice dislocations can depend on the grain size.     

Dependence of the longitudinal relaxation time of the polarization of cesium atoms in the ground state on the temperature of an antirelaxation coating

The dependence of the time of longitudinal relaxation of the ground-state cesium vapor on the temperature of the antirelaxation coating of the cell walls is studied experimentally. It is found that the fast component of relaxation is independent of the coating temperature, while the slow component depends on it. The temperature dependence of the slow relaxation component is used to estimate the energy of activation of desorption of cesium atoms from the antirelaxation coating, E _desorp = 0.13 eV.     

Generalized Elliott-Yafet theory of electron spin relaxation in metals: origin of the anomalous electron spin lifetime in MgB2

The temperature dependence of the electron-spin relaxation time in MgB2 is anomalous as it does not follow the resistivity above 150 K; it has a maximum around 400 K and decreases for higher temperatures. This violates the well established Elliot-Yafet theory of spin relaxation in metals. The anomaly occurs when the quasiparticle scattering rate (in energy units) is comparable to the energy difference between the conduction and a neighboring bands. The anomalous behavior is related to the unique band structure of MgB2 and the large electron-phonon coupling. The saturating spin relaxation is the spin transport analogue of the Ioffe-Regel criterion of electron transport.     

Spin-lattice relaxation of deuterated methyl groups: Implications of the pauli principle

The high-field spin-lattice relaxation of deuterated methyl groups undergoing rotational tunneling is investigated theoretically. It is found that for systems showing a tunneling frequency comparable to accessible Larmor frequencies the relaxation to equilibrium of the Zeeman energy does not follow a simple exponential time dependence even in powdered samples due to a finite coupling to the relaxation of the tunneling system. This finding contrasts to the high-temperature behavior of reorienting methyl groups which undergo simple exponential relaxation. The nonexponentiality has its origin in the statistical coupling of the three deuteron spins due to the Pauli principle.     

Relaxation model of the orientational phase transition in fullerite C60

The model of thermal behavior of a thermoelastic medium is developed in the context of the Landau theory of phase transitions. In the framework of this model, two different problems are considered with allowance for order parameter relaxation: the problem of relatively slow uniform heating (cooling) of the medium under external hydrostatic pressure and the problem of order parameter relaxation at thermal isolation. A finite value of the relaxation constant τ of the order parameter is demonstrated to bring about the heating (cooling) rate dependence of the physical quantities, such as specific heat. The relaxation time of the order parameter is shown to be twice larger than the temperature relaxation time, as a consequence of the Landau expansion of the free energy.     

气体声弛豫过程中有效比热容与弛豫时间的分解对应关系

声在多原子分子气体中传播所引起的弛豫过程是探索气体特性的重要方面. 本文通过研究气体声弛豫过程中振动自由度与平动自由度(V-T)以及振动自由度之间(V-V)的分子能量转移模型, 给出了有效比热容与弛豫时间的分解对应关系及其通用获得方法. 该分解模型与现有的声弛豫模型相比, 反映了分解后的V-T 和V-V弛豫过程中振动比热容与弛豫时间的对应关系, 并发现了较高能级是引起对应声弛豫过程的决定因素. 将基于该分解模型获得的气体声弛豫衰减谱经碰撞直径微调改进后, 比现有理论更接近实验数据, 其结果证明了该分解对应关系的正确性和合理性.     

Temperature relaxation and energy loss of hot carriers in graphene

The temperature relaxation and energy loss of hot Dirac fermions are investigated theoretically in graphene with carrier–optical phonon scattering. The time evolutions of temperature and energy loss for hot Dirac fermions in graphene are calculated self-consistently. It shows that the carrier–optical phonon coupling results in the energy relaxation of hot carriers excited by an electric field, and the relaxation time for temperature is about 0.5–1 ps and the corresponding energy loss is about 10–25 nW per carrier for typically doped graphene samples with a carrier density range of 1–5×10¹² cm^?2. Moreover, we analyze the dependence of temperature and energy relaxation on initial hot carrier temperature, lattice temperature and carrier density in detail.     

Energy relaxation mechanism in Landau level system of quantum wells

Kinetics of intrasubband energy relaxation of electrons in the system of Landau levels lying below the optical phonon energy is studied. Extraordinary behavior of the relaxation of electronic subsystem excitation energy is detected. Despite the fact that its main channel is optical phonon emission, the total relaxation time exceeds the characteristic times of scattering on optical phonons by several orders of magnitude.     

Statistics of deep energy states in Coulomb glasses

We study the statistics of local energy minima in the configuration space and the energy relaxation due to activated hopping in a system of interacting electrons in a random environment. The distribution of the local minima is exponential, which is in agreement with extreme value statistics considerations. The relaxation of the system energy shows logarithmic time dependence reflecting the ultrametric structure of the system.     

Rotational reorientation of the director in twisted nematic liquid-crystal cells

The orientational relaxation of the director to its equilibrium orientation under electric, elastic, and viscous torques arising in twisted nematic liquid-crystal cells is investigated. It is shown that the relaxation time of the director depends strongly on the external electric field strength and weakly on the energy of anchoring of liquid-crystal molecules to the surfaces of the cell. The relaxation time of the director anomalously increases in electric fields close to the Fréedericksz threshold. It is established that, at specific strengths of the external electric field, the relaxation can occur in the form of traveling waves propagating from one edge to the other edge of the twisted nematic liquid-crystal cell. The calculations of the relaxation processes in the vicinity of the nematic-smectic A phase transition temperature demonstrate that the distortion of the director field is uniform over the entire cross section of the liquid-crystal cell and does not depend on the strength of anchoring of the liquid-crystal molecules to the surfaces of the cell.     

多元可激发气体声弛豫频率的环境影响分析

推导多元可激发气体中声弛豫频率和环境温度、压强的解析关系.理论分析和仿真计算表明：声弛豫频率线性反比于主弛豫过程的弛豫时间,正比于主弛豫过程的振动耦合热容,反比于外自由度热容;温度升高导致振动耦合热容增加、内外自由度能量转移速率增大引起弛豫时间减少,进而造成声弛豫频率正比于环境温度;压强增加使得分子碰撞速率增加引起弛豫时间减少,进而使得声弛豫频率线性正比于环境压强.