The vortex physics which comes from the vortex core

A theoretical view of vortex core states and of their effects on physics of vortices in clean s- and d-wave-type II superconductors is presented based on a semi-classical picture of a vortex core as an Andreev potential well containing many quasiparticle states. We discuss the density of states, the vortex dissipation, Hall effect, and the vortex mass. The dynamic characteristics are determined by relaxation of core excitations driven by a moving vortex. In a d-wave superconductor, gap nodes make the core states more extended and introduce novel features into thermodynamics and kinetics of vortices.     

Long time behavior in the quantized standard map with dissipation

A dissipative version of the quantized standard map is constructed by analytical means and iterated numerically to study the long time behavior in various regions of the damping rate. For weak dissipation, stochastic transitions induced by the heat bath disrupt the localization in the action variable, which suppresses chaotic motion in the conservative quantized standard map, and tend to restore diffusion of action. A steady state is reached on the time scale of classical relaxation. For strong dissipation, observable deviations from classical behavior both in the transients and in the statey state are due to quantum noise. They are reproduced by a classical stochastic map which is approached by the dissipative quantum map as its semi-classical limit.     

Ultrafast electron spin dynamics in bulk CdTe investigated by femtosecond pump-probe reflection spectroscopy

The transient spin polarization dynamics in bulk cadmium telluride (CdTe) at 70 K is investigated by the circularly polarized pump-probe reflection technique. A general expression is derived from the rate equations of a two-level system with small signal approximation to describe the light-helicity-dependent reflection spectrum. The initial degree of electron spin polarization in the excited state and the electron spin relaxation time in bulk CdTe at low temperature with different carrier density are analyzed according to this model. Our experimental results reveal that the D?yakonov–Perel? mechanism based on a fully microscopic kinetic spin Bloch equation (microscopic KSBE) approach dominates in the electron spin relaxation process in bulk CdTe crystal.     

Quantum tunneling: A general study in multi-dimensional potential barriers with and without dissipative coupling

Quantum tunneling is formulated in terms of the time evolution of a localized state and thus shown to be dependent upon the eigenspectrum of the system Hamiltonian. A number of exactly solvable models with local and non-local double-well potentials are discussed, and it is shown how, for local potentials, other solvable models can be generated by using Gelfand-Levitan and Darboux transformations. Tunneling in multi-dimensional potential barriers is investigated under semi-classical approximation by developing the method of asymptotic expansion of the wave function for large quantum numbers and the WKB approximation for separable systems. General expressions for the imaginary-time tunneling trajectory are obtained in both methods and specific applications are discussed. Approximation schemes for non-separable systems are also presented. A general study of dissipative multi-dimensional tunneling is carried out by using the Gisin equation, the Schrödinger-Langevin equation and the complex potential model. It is shown that, in general, different models of dissipation are not equivalent in the tunneling context. Using these models one can show (a) the existence of critical damping beyond which no tunneling can occur, (b) that tunneling trajectories are dependent on the damping constant and (c) that dissipation may stabilize the excited state rather than the ground state. Finally the tunneling time delay in one-dimensional systems for undamped and for dissipative systems is formulated in terms of the phase shift, and this has been used to show that the effect of damping on the time delay is ignorable.     

Hierarchic Natures and Dynamics of Photoinduced Structural Phase Transition in Non-Degenerate Charge Density Wave States Via Successive Photoexcitations

We investigate the adiabatic and dynamical natures of the lattice relaxation of excitons in strongly coupled electron-phonon (e-ph) systems using the extended Peierls-Hubbard model, so as to clarify the possible mechanisms of the photoinduced structural phase transition (PISPT) via multi-photon. Focusing on the growth process of relaxed domains that is induced by multi-photoexcitation, we calculate the adiabatic potential energy surfaces relevant to the nonlinear lattice relaxations of excitons in this process. Calculated potentials lead to an essential model of a multi-stepwise potential-crossing (MSPC) system that is composed of many displaced harmonic oscillators as an elementary process of the domain growth in the strongly coupled e-ph systems. We also investigate the dynamical natures in such MSPC systems calculating the time-developments the excited wave packet in this system using the density operator. It is concluded from calculated results that the system possibly develops from the lowest-energy potential state to the higher ones by the effect of the photoexcitations followed by the lattice relaxations.     

Lack of partial thermal equilibrium in pinch discharges

Measurements of the deuterium Balmer line intensities in the early phase of a theta pinch discharge show strong deviations from steady state population of levels considerably above the collision limit, even if criteria for the relaxation times of these levels are well satisfied. Solutions of time dependent rate equations for a hydrogen plasma confirm these observations. In cases of rising electron temperatures and rising degree of ionization the population of the ground level deviates by orders of magnitude from the steady state population of the momentary electron temperature and density. The population rates from the highly overpopulated ground level into levels above the collision limit then successfully compete with population rates from other levels and the continuum. Under such circumstances the relaxation time of excited levels above the collision limit into thermal equilibrium is determined by the relaxation time of the ground level into its steady state population.     

Dynamical potential approach to dissociation of H--C bond in HCO highly excited vibration

The highly excited vibrational levels of HCO in the electronic ground state, \tilde {X}¹A',are employed to determine the coefficients of an algebraic Hamiltonian, by which the dynamical potential is derived and shown to be very useful for interpreting the intramolecular vibrational relaxation (IVR) which operates via the HCO bending motion. The IVR inhibits the dissociation of H atom and enhances the stochastic degree of dynamical character. This approach is from a global viewpoint on a series of levels classified by the polyad number which is a constant of motion in a certain dynamical domain. In this way, the seemingly complicated level structure shows very regular picture, dynamically.     

激发态之间的电离与复合过程对类氖锗19.6nm X射线激光增益系数的影响

考察了激发态之间的电离与复合过程对等离子体状态的影响,并对其原因进行了细致的分析,分别考察了对1.0ns,100ps和5ps激光驱动的类氖锗19.6nm Ｘ射线激光增益系数的影响.研究表明,对于5ps激光驱动的瞬态机理X射线激光来讲,因增益区处在高密度区,所以,激发态之间的电离与复合过程对X射线激光将不可以忽略.对于1.0ns和100ps激光驱动的亚稳态机理X射线激光来讲,在电子密度小于等于5×10²⁰cm^－3的区域,忽略激发态之间的电离与复合使增益的时间半高全 关键词： X射线激光 矩阵分块法 类氖锗 双电子激发态     

紧聚焦飞秒脉冲与石英玻璃相互作用过程中的电子动量弛豫时间研究

本文通过数值模拟(3+1)维扩展的广义非线性薛定谔方程,研究了紧聚焦飞秒激光脉冲在诱导石英玻璃的非线性电离过程中电子动量弛豫时间对于该电离过程的影响.计算结果证明电子动量弛豫时间会直接影响入射脉冲在焦点区域所形成的峰值场强、自由电子态密度和能流等参量的分布态势,因此在与实验结果相比较后发现适合于相互作用过程的电子动量弛豫时间的理论值约为1.27 fs.进一步的研究表明,电子动量弛豫时间与逆韧致吸收效应、雪崩电离的概率、等离子体密度、等离子体的自散焦效果以及间接引起的焦平面位置的移动都有着密切的联系.当前的研究结果表明电子动量弛豫时间在飞秒激光脉冲与物质相互作用的过程中发挥着重要作用.     

Correlations in alpha-alpha scattering and semi-classical optical models

We show the equivalence of semi-classical solutions to optical model coupled-channel equations derived from Watson's form of the nucleus-nucleus multiple-scattering series to the Glauber multiple-scattering series. A second-order solution to the semi-classical coupled-channel elastic amplitude is shown to be nearly equivalent to a second-order optical-phase-shift approximation to the Glauber amplitude if the densities of all nuclear excited states are approximated by the ground-state density. Using the Jastrow method to model the two-body density we find an average excited-state density to be of negligible importance in the double-scattering region of alpha-alpha scattering.     

Non-linear dynamics of a driven two-level tunnelling defect

With increasing external-field amplitude the dynamics of a driven two-level system shows a cross-over from the weak-coupling or linear-response behaviour to a non-linear regime which is characterised by the appearance of Rabi oscillations, a field-dependent dynamical susceptibility, saturation of energy dissipation and additional frequencies in the correlation function. The system any initial distribution will relax towards a stationary state with a time-dependent polarisation vector. These features are derived from the propagator of the two-level system which is calculated using a perturbative scheme with a well-defined small parameter; the roatating-wave approximation of the Bloch equations is avoided. the dynamical behaviour is discussed by means of correlation and response functions.     

Attosecond plasma wave dynamics in laser-driven cluster nanoplasmas

We introduce a microscopic particle-in-cell approach that allows bridging the microscopic and macroscopic realms of laser-driven plasma physics. As a first application, resonantly driven cluster nanoplasmas are investigated. Our analysis reveals an attosecond plasma-wave dynamics in clusters with radii R is approximately equal to 30 nm. The plasma waves are excited by electrons recolliding with the cluster surface and travel toward the center, where they collide and break. In this process, energetic electron hot spots are generated along with highly localized attosecond electric field fluctuations, whose intensity exceeds the driving laser by more than 2 orders of magnitude. The ionization enhancement resulting from both effects generates a strongly nonuniform ion charge distribution. The observed nonlinear plasma-wave phenomena have a profound effect on the ionization dynamics of nanoparticles and offer a route to extreme nanoplasmonic field enhancements.     

Off-diagonal long-range order and currents in weakly coupled superconductors

Within the framework of quasi equilibrium approximation, Josephson’s expression for current in a weakly coupled superconducting system is derived without the use of any specific microscopic model. It is based only on the existence of the off-diagonal long-range order in the two-particle reduced density matrix. Allowing for deviations from the quasi equilibrium approximation, generalised Josephson equations are obtained which include ohmic terms. The effect of relaxation and thermal fluctuations is examined in detail to emphasise the physical origin of various terms in the expression for current.     

Molecular coherence effects in stimulated raman scattering

A semi-classical calculation of the three-level system consisting of the ground state, the vibrationally excited state and the electronic excited state under the laser and the Stokes perturbation is given. The induced molecular polarization produces gain modulation of the Stokes and loss modulation of the laser at a frequency that is dependent on the optical intensity. With the optical intensity in self-trapped filaments in nonlinear liquids such as CS₂, the period of modulation becomes of the order 10^?11 s and a large amplitude modulation of the laser and the Stokes waves will result. The amplitude modulation is not much reduced, if the molecular relaxation time of the order 10^?11 s is taken into account. Effects of non-uniform field distribution and the width and shape of the incident laser pulse are discussed. The frequency broadening caused by the three-level effect is shown to be larger than, or at least as large as, the broadening caused by the optical Kerr effect.     

Relaxation of Excited States in C60

The static study has shown that the excited state with electron-hole pair in C₆₀ can cause the distortion of the bond structure to form a polaron-like exciton with symmetry D_5d. This paper further reveals the relaxation process from the initial electron-hole pair state to the polaron-like exciton by solving the dynamical equations. The relaxation time of this dynamical process can be determined from the time-dependent bond distortion with time step 4 femtoseconds.     

Time‐resolved random laser spectroscopy of inhomogeneously broadened systems

The understanding of energy transfer processes in biological systems occurring among optical centres which exhibit inhomogeneously broadened spectral bands is of paramount importance to determine time constants and spatial distribution of energy flow. A new time resolved‐spectroscopy based on the random laser generation of the optical probes is reported. As an example, the excited state relaxation of Rhodamine B molecules in an organic‐inorganic hybrid material is investigated. This kind of spectroscopy may resolve not only the spectral features of the system but also provide a high speed picture of the energy transfer and excited state relaxation of the involved optical probes. The results could be applied to other kind of efficient interacting chromophore pairs embedded in inhomogeneous scattering structures such as biological tissues.     

Non-linear Relaxation of the Photo-induced High Spin State in Spin-Crossover Solids: Effect of Correlations

We investigate a microscopic model based on the pair approximation, for the dynamical properties of the photo-induced high-spin state in spin-crossover solids at low temperature. The model uses the Ising-like hamiltonian and combines long- and short-range interactions. The stochastic treatment of the latter provides a set of two coupled differential equations for the macroscopic short- and long-range order parameters, which reproduce successfully the main features of the experimental relaxation curves.