非对称量子点中强耦合磁极化子激发态的性质

采用线性组合算符和幺正变换方法,研究非对称量子点中强耦合磁极化子的激发态性质。导出强耦合磁极化子的第一内部激发态能量、激发能量和从第一内部激发态到基态的跃迁谱线频率随量子点的横向和纵向有效受限长度、磁场的回旋频率和电子-声子耦合强度的变化关系。数值计算结果表明：第一内部激发态能量、激发能量和跃迁谱线频率随磁场的回旋频率和电子-声子耦合强度的增加而增大.随量子点的横向和纵向有效受限长度的减小而迅速增大,表现出奇特的量子尺寸效应。     

On some peculiarities of propagation of weak electromagnetic pulses in Bose-Einstein condensates of alkali-metal atoms

We study theoretically the linear response of a gas in the state with Bose-Einstein condensate to the perturbation by an external electromagnetic field (weak laser pulse). The Green’s functions formalism is used to study the dispersion characteristics of a system at finite temperatures. It is shown that the group velocity of the near-resonant pulses in condensate in some cases can strongly depend on the temperature. Basing on the account of the Zeeman splitting of the magnetic states we study also a possibility to filter light pulses by the condensate with several occupied quantum states.     

Wave spectra in solid and liquid complex (dusty) plasmas

Spectra of longitudinal and transverse waves were obtained experimentally in liquid and solid two-dimensional complex (dusty) plasmas at different kinetic temperatures. As the temperature increased and the phase state of the plasma changed from solid to liquid, the phonon spectra of both longitudinal and transverse modes broadened (especially at high wave numbers), indicating increased damping. The transverse mode disappeared and a thermal (compressional) mode appeared.     

Ab initio study of the structure and dynamical properties of crystalline ice

We investigated the structural and dynamical properties of a tetrahedrally coordinated crystalline ice from first principles based on density functional theory within the generalized gradient approximation with the projected augmented wave method. First, we report the structural behaviour of ice at finite temperatures based on the analysis of radial distribution functions obtained by molecular dynamics simulations. The results show how the ordering of the hydrogen bonding breaks down in the tetrahedral network of ice with entropy increase, in agreement with the neutron diffraction data. We also calculated the phonon spectra of ice in a 3× 1× 1 supercell using the direct method. So far, due to the direct method used in this calculation, the phonon spectra are obtained without taking into account the effect of polarization arising from dipole–dipole interactions of water molecules, which is expected to yield the splitting of longitudinal and transverse optic modes at the Γ point. The calculated longitudinal acoustic velocities from the initial slopes of the acoustic mode are in reasonable agreement with the neutron scattering data. Analysis of the vibrational density of states shows the existence of a boson peak at low energy of the translational region, a characteristic common to amorphous systems.     

Locality and currents for the dual string

We wish to describe the coupling of a local current to the dual string as the amplitude for the string to collapse to a point. At the quantum level we note that states which are localized in the transverse directions are forced by the gauge constraints to have longitudinal extension. The best we can do in the conventional model is, therefore, to construct off-shell states which have zero helicity (but no unique spin). We calculate the propagator for such states and compare it with the model of Schwarz. In their respective critical dimensions (26 for the string and 16 for the off-shell model of Schwarz) the two results become identical. We also calculate the Green functions for the coupling of one of our off-shell states to any number of on-shell particles by means of the functional formalism. Our results have a close connection with the previous models of Schwarz and Wu and of Corrigan and Fairlie.     

Liquid ground state, gap, and excited states of a strongly correlated spin chain

We present an exact solution of an experimentally realizable and strongly interacting one-dimensional spin system which is a limiting case of a quantum Ising model with long range interaction in a transverse and longitudinal field. Pronounced quantum fluctuations lead to a strongly correlated liquid ground state. For open boundary conditions the ground state manifold consists of four degenerate sectors whose quantum numbers are determined by the orientation of the edge spins. Explicit expressions for the entanglement properties, the exact excitation gap, as well as the exact wave functions for a couple of excited states are analytically derived and discussed. We outline how this system can be experimentally realized in a lattice gas of Rydberg atoms.     

Current correlation functions of ideal fermi gas at finite temperature

Expressions for transverse and longitudinal current-current correlation functions of an ideal Fermi gas describing the current fluctuations induced in the electron system by external probe perpendicular and parallel to the propagation of electron wave, have been obtained at finite temperature. The results obtained for transverse and longitudinal functions are presented for different values of wavelength and frequency at different temperatures. The diamagnetic susceptibility as a function of temperature has also been obtained from transverse current correlation function as its long wavelength and static limit, which smoothly cross over from known quantum values to the classical limit with increase in temperature.     

Normal modes of a relativistic quantum plasma; The one-component plasma

The normal modes of a relativistic electron gas are studied on the basis of the Boltzmann-Vlasov kinetic equation via a projection operator formalism. A general framework is constructed in which the fully relativistic Vlasov self-consistent force term appears as a symmetric operator acting in the Hilbert space of one-particle states. The plasma-dynamical equations are obtained by projecting onto the subspace consisting of the charge, energy and momentum densities, plus the nonconserved current density. The eigenmodes of these equations include two transverse and two longitudinal plasma modes, and one damped heat mode. They are explicitly calculated up to second order in the wave vector and to first order in the collision frequency.     

Gauge independent gravitationally-coupled electromagnetic field

We give a totally 3-covariant formulation of the gravitationally coupled electromagnetic field (with a source) in terms of physical 3-covariant variables, keeping the correspondence with the A.D.M. formulation of the problem. We introduce a 3-covariant time derivation which allows us to discuss the spreading of the transverse and longitudinal components of the electromagnetic field. Then we present the second-order propagation equation and the Hamiltonian 3-covariant equations in a complete electromagnetic gauge independent fashion using the well-known elliptic operator Δ(g _ij ) and we also discuss the dynamical impossibility of disentangling the transverse and longitudinal modes. Thereafter we extend the 3-covariant formulation to the gravitational field and consider the problems of the initial conditions for the full system, as done by York for the vacuum case. Finally, we apply the formalism to the merostatic sourceless problem, showing the connection between the merostatic and the static cases.     

Polarized photoluminescence excitation spectroscopy of single-walled carbon nanotubes

The polarized photoluminescence excitation spectra of twenty-five single-walled carbon nanotube species are reported. For light polarized along the nanotube axis, the main absorption resonance at E22 shows sidebands attributed to phonon assisted absorption. Sidebands to E11 have a diameter dependent energy and are assigned to excited excitonic states. Along with longitudinal excitations, several transverse excitations are identified. The transverse E12 resonance has a specific family pattern with energy close to E22. Comparison with theory provides an estimate of the strength of the Coulomb interaction.     

Discrete solitons in inhomogeneous waveguide arrays

The existence and dynamical properties of discrete solitons in inhomogeneous waveguide arrays with a Kerr nonlinearity are studied in two different configurations. First we investigate the effect of a longitudinal periodic modulation of the coupling strength on the dynamics of discrete solitons. It is shown that resonances of internal modes of the soliton with the longitudinal structure may lead to soliton oscillations and decay. Second we study the existence and stability of discrete solitons in arrays exhibiting a linear variation of the waveguide effective index in the transverse direction. We find that resonant coupling between conventional discrete solitons and linear Wannier-Stark states leads to the formation of so-called hybrid discrete solitons.     

Thermally driven spin transport through a transverse-biased zigzag-edge graphene nanoribbon

In the framework of the Landauer-Büttiker formalism, we investigate coherent spin transport through a transverse-biased magnetic zigzag-edge graphene nanoribbon, with a temperature difference applied between the source and the drain. It is shown that a critical source temperature is needed to generate a spin-polarized current due to the presence of a forbidden transport gap. The magnitude of the obtained spin polarization exceeds 90% in a wide range of source temperatures, and its polarization direction could be changed by reversing the transverse electric field. We also find that, at fixed temperature difference, the spin-polarized current undergoes a transition from increasing to decreasing as the source temperature rises, which is attributed to the competition between the excited energy of electrons and the relative temperature difference. Moreover, by modulating the transverse electric field, the source temperature and the width of the ribbon, we can control the device to work well for generating a highly spin-polarized current.     

铁氧体参量耦合振荡的理论分析

在本文中我们系统地讨论了铁氧体小样品在超高频电源的激发下产生参量振璗的耦合关系,指出激发机构应分为磁场驱动和磁化驱动二类。前者的特例为Denton新近发现的,使用空间均匀的纵向注入场;后者的特例为Suhl最早所研究的,使用空间均匀的横向注入场所激发的一致进动的磁化向量为驱动力。从静磁势函数的耦合微分方程我们得到这二种特殊注入方式激发的静磁势函数的完全解(一次近似),表达为Walker函数的线性组合,在边界连续的要求下,这些势函数中的Walker模只在它们的指标之间适合一定的条件时才相互关联。当直流磁场调谐于一对Walker模时,耦合的静磁势简化为静磁操作的势函数。我们具体分析了静磁操作参量振璗从注入场吸取的功率,根据后者必须不为零才可能产生参量振璗,我们推导出空间均匀场激发一对静磁模的选择定则,恰与从边界连续推出的关联条件完全相同,并且进一步得到空间不均匀场激发一对静磁模的选择定则。我们指出,参量振璗的振幅的决定必须引用能量守恒和量子数相等的方程。最后我们采用Suhl的方法推算出空间均匀的纵向注入场的激发临阈强度,并且讨论了这一方法的近似性质。     

Dynamical structure functions,collective modes,and energy gap in charged-particle bilayers

The dynamical properties of strongly coupled charged-particle bilayers are investigated by molecular dynamics (MD) simulation and theoretical analysis. The spectra of the current correlation functions show the existence of two (in-phase and out-of-phase) longitudinal and two (in-phase and out-of-phase) transverse collective modes. The out-of-phase modes possess finite frequencies at wave numbers k-->0, confirming the existence of the predicted long-wavelength energy gap in the bilayer system. A theoretical model based on an extended Feynman ansatz for the dynamical structure functions provides predictions on the strength of the collective modes that are verified by the MD experiment.     

Effects of temperature on the relaxation to equilibrium and stationary nonequilibrium states of some Langevin systems

We investigate the effects of temperature on the properties of the time relaxation to equilibrium and nonequilibrium steady states of correlation functions of some Langevin harmonic systems. We consider commonly used dissipative and conservative Langevin dynamics, and show that the time relaxation rate depends on the temperature in the case of thermal reservoirs at different temperatures connected to the system, but it does not happen in the case of relaxation to equilibrium, i.e., if all the heat bath are at the same temperature. Our formalism maps the initial stochastic problem on a noncanonical quantum field theory, and the calculations of the relaxation rates are based on a perturbative analysis. We argue to show the reliability of the perturbative computation.     

An introduced effective-field theory study of spin-1 transverse Ising model with crystal field anisotropy in a longitudinal magnetic field

A spin-1 transverse Ising model with longitudinal crystal field in a longitudinal magnetic field is examined by introducing an effective field approximation (IEFT) which includes the correlations between different spins that emerge when expanding the identities. The effects of the crystal field as well as the transverse and longitudinal magnetic fields on the thermal and magnetic properties of the spin system are discussed in detail. The order parameters, Helmholtz free energy, entropy and specific heat curves are calculated numerically as functions of the temperature and Hamiltonian parameters. A number of interesting phenomena such as reentrant phenomena originating from the temperature, crystal field, transverse and longitudinal magnetic fields have been found.     

Transverse wave band gaps and longitudinal wave band gaps in solid phononic crystals

Based on the properties of transverse (divergenceless) waves and longitudinal (irrotational) waves, we divided the transverse wave modes and longitudinal wave modes from the mixed eigen modes in solid phononic crystals. By investigating the transverse wave and longitudinal wave band structures at low frequency, we found that transverse bands and longitudinal bands exhibit different behaviors in solid systems including spherical scatterers. Phononic crystal with a large density ratio of solid spheres to the background can guarantee both the large longitudinal and large transverse band gap, but solid spheres with a small ratio of longitudinal wave velocity to transverse wave velocity can only help to enlarge the longitudinal band gap, and do not help to enlarge the transverse band gap.     

Quantum nonlocality for two-mode correlated states based on generalized pseudospin operators

In this Letter, we investigate the quantum nonlocality of two-mode correlated states. We find that the pseudospin formalism [Z.B. Chen, J.W. Pan, G. Hou, Y.D. Zhang, Phys. Rev. Lett. 88 (2002) 040406] generally fails to depict the nonlocality of the states when the photon number difference between the two modes is odd. The formalism is then generalized such that the nonlocality of a two-mode correlated state can be well revealed without regard to the difference. Later we consider the nonlocality of the two-mode intelligent SU(1,1) states in the generalized formalism and compare our results with the entanglement of the corresponding states.