Multiferroic phase transitions in manganites RMnO3: A two-orbital double exchange simulation

The semi-quantum two-orbital exchange model is used to investigate the effect of small rare-earth ion substitution on orthorhombic RMnO 3 with A-type antiferromagnetic order,using the Monte Carlo algorithm,exact diagonalization,and zero-temperature optimization approaches.It is revealed that the substitution results in a rich multiferroic phase diagram where the coexisting A-type antiferromagnetic phase and spiral spin phase,pure spiral spin phase,coexisting spiral spin phase,the E-type antiferromagnetic phase,and the pure E-type antiferromagnetic phase emerge in sequence.The multiferroic phase transitions modulate substantially the electric polarization,which is consistent qualitatively with recent experiments.     

Monopole Charge Domain in High-Gain Gallium Arsenide Photoconductive Switches

Considering that semi-insulating gallium arsenide photoconductive switches can be triggered into the high gain mode and no reliable theories can account for the observed transient characteristics,we propose the monopole charge domain model to explain the peculiar switching phenomena occurring in the high gain mode and we discuss the requirements for the lock-on switching.During operation on this mode,the applied field across the switch and the lock-on field are all larger than the Gunn threshold field.Our developed monopole charge domain is based on the transferred-electron effect,but the domain is only composed of large numbers of electrons piled up due to the negative differential mobility.Using the model and taking the physical mechanism of the avalanche impact ionization and recombination radiation into consideration,we interpret the typical phenomena of the lock-on effect,such as the time delay between the beginning of optical illumination and turning-on of the switch,and the conduction mechanism of the sustaining phase.under different conditions of bias field intensity and incident light energy,the time delay of the switching is calculated.The results show that the physical mechanisms of impact ionization and recombination radiation occurring in the monopole charge domain are responsible for the lock-on switching.     

Analyzing Affect of Image Charge in Space Charge Effect

There is an increasing requirement of high injection current and highly charged ion beams for accelerators at many laboratories, such as CERN, GSI, GANIL and IMP, with the development of super-conducting ECR source in recent.years. In this case, the space charge effect becomes a major concern when the beam current is as high as tens of mA. In fact, the faradic field induced by the image charges will be come into the metallic surfaces while the beams are transported in a vacuum tube or in between two plates. In order to ensure studying the space charge effect in reason, it is necessary to investigate the effect from such a field.     

Massive Quark Propagator in the Colour—Superconducting Phase

A more general expression for the quark propagator including both chiral and diquark condensates has been derived by using energy projectors.This makes it possible to study the phase transition from the hadron phase to the colour-superconductivity phase in the moderate baryon density region by using the Feynman diagrammatic method or the Green function method.     

In—Phase Resonances with Generic Transmission Zeros and Eigenvectors of Hamiltonian in Models of Single Channel Transport

We investigate the phase coherent transport in a single channel system.The theory that the tranmission zeros lead to abrupt phase change and in-phase resonances in confirmed numerically in two tight-binding models.After calculating the eigenvalues and eigenvectors of the Hamiltonians we also confirmed that the same symmetry of the eigenvectors also leads to the abrupt phase change and in-phase resonances that equal the transmission zero.     

Quantum Phase Transitions,Entanglement Spectrum,and Schmidt Gap in Bond-Alternative S=1 Antiferromagnetic Chain

Bipartite entanglement, entanglement spectrum, and Schmidt gap in S=1 bond-alternative antiferromagnetic Heisenberg chain are investigated by the infinite time-evolving block decimation （iTEBD） method. The quantum phase transition （QPT） from the singlet-dimer phase to the Haldane phase can be detected by the singular behavior of bipartite entanglement, the sudden change of the entanglement spectrum, and the completely vanishing of the Schmidt gap. The critical point is determined to be around rc ~- 0.587, and the second-order character of the QPT is verified. Doubly degenerate entanglement spectra of both even and odd bonds are observed in the Haldane phase, by which one can distinguish the Haldane phase from the singlet-dimer phase easily. Nearest-neighbor antiferromagnetic correlations and next-nearest-neighbor ferromagnetic correlations are found in the whole parameter region. At the critical massless point, although exponentially decaying antiferromagnetie correlation is observed, it approaches to a constant value finally. Therefore, long-range correlations exist and the correlation length becomes divergent at the critical point.     

Evolutions of Yang Phase Under Cyclic Condition and Adiabatic Condition

There are three non-integrable phases in literatures： Berry phase, Aharonov-Anandan phase, and Yang phase. This article discusses the evolutions of Yang phase under the cyclic condition and the adiabatic condition for the general time-dependent harmonic oscillator, thus reveals the intimate relations between these three non-integrable phases.     

Weak Finite—Size Dependence of Velocity and Strong Phase Dependence of Central Charge

We study the finite-size scaling behavior of velocity and central charge for different coupling constants and different phases in (1 1)-dimensional lattice model in very short chains.Using XXZ spin 1/2 chains with 15 or fewer sites,we demonstrate the weak finite-size dependence of spinon velocity for any magnitude of coupling strength Jz and the strong phase dependence of central charge.This behavior of velocity and central charge in different coupling constants and different phases gives a method to determine phase transitions of (1 1)-dimensional models.This method is simple and efficient by utilizing only the ground state energy of very short finite-size chains.It is also general and powerfur for various one-dimensional lattice models and it uncovers eventhe weakest berezinski-Kosterlitz-Thouless phase transitions.     

Evolution of Bond-Order-Wave Phase in One-Dimensional Mott Insulators

In this paper, by using the level spectroscopy method and bosonization theory, we discuss the evolution of the bond-order-wave （BOW） phase in a one-dimensional half-filled extended Hubbard model wlth the on-site Coulomb repulsion U as well as the inter-site Coulomb repulsion V and antiferromagnetic exchange J. After clarifying the generic phase diagrams in three limiting cases with one of the parameters being fixed at zero individually, we find that the BOW phase in the U-V phase diagram is initially enlarged as J increases from zero but is eventually suppressed as J increases further in the strong-coupling regime. A three-dimensional phase diagram is suggested where the BOW phase exists in an extended region separated from the spin-density-wave and charge-density-wave phases.     

Discontinuous Structural Phase Transition Behaviour in Multiple Component Alloy Melts

Discontinuous structural phase transition behaviour in seven kinds of liquid multiple component alloys are found by using a torsional oscillation viscometer. There are different phases existing in the system and the number of phases is discussed using the equilibrium thermodynamics phase rule. The phase parameters （ηo,ε） and order parameter dI in different phase regions are calculated based on the researched results. It is found that the parameters （ηo,ε, df） change at the structural transition point. The diameter of the fluid clusters, di, is stable in each phase region, which indicates that the structure is uniform.     

Phase—Locking Dynamics in Coupled Circle—Map Lattices

The phase-locking dynamics in 1D and 2D lattices of non-identical coupled circle maps is explored.A global phase locking can be attained via a cascade of clustering processes with the increase of the coupling strength.Collective spatiotemporal dynamics is observed when a global phase locking is reached.Crisis-induced desynchronization is found,and its consequent spatiotemporal chaos is studied.     

Effects of Charge Transfer Agents on the Holographic Parameters of a Photopolymer

The principle of charge transfer agents was investigated experimentally.There is a compensation effect between triethanolamine (TEA) and diphenyliodonium hexafluorophosphate (DPI) in the polymerization process of a photopolymer.The experimental results illustrate that TEA has a stronger effect in the initial stage of exposure,and DPI has a stronger effect during the propagation stage of the polymerization process.We explain the main contributions of DPI in the superadditive photopolymer kinetics that results in an obvious increase of sensitivity.     

Charge exchange in collisions of H2^＋ with H^-

The process of mutual neutralization in slow H2^＋ H^- collisions is considered within the multi-channelLandau-Zener model. The calculated total mutual neutralization cross section is in satisfactory agreement with theexperimental data available in the CM energy range 20-2000 eV.     

Moessbauer Investigation of the Ferromagnetic Coupling in Copper-Iron Polycyanides

One of the Prussian blue analogs, molecular magnet Cu3^Ⅲ [Fe^Ⅲ (CN)6]2.11.6H2 O, was investigated by Moessbauer spectroscopy. It was found that transition temperature was around Tc = 18.5 K from paramagnetic phase to ferromagnetic phase. The β value of the critical exponent is around 0.338 at magnetic ordering temperature.Therefore, the ferromagnetic coupling interaction of Cu-Fe cyanide could be clearly explained by spin wave theory.     

An investigation of phase separation by magnetic force microscopy in La0.45Sr0.55MnO3-δ(δ≈0.01)

We have found phase separation in La_0.45Sr_0.55MnO_3-δ (LSMO) by means of electron spin resonance, magnetic force microscopy (MFM) and magnetic measurements. Ferromagnetic and antiferromagnetic phases can coexist at low temperatures, and ferromagnetic and paramagnetic phases coexist when the temperature lies between the Néel and Curie temperatures. The size and shape of the ferromagnetic phases (the minority phases) was first observed directly from MFM images. It is suggested that the phase separation in LSMO is not the charge segregation type, but an electroneutral type due perhaps to the nonuniform distribution of oxygen vacancies.     

The geometric phase of the quantum systems with slow but finite rate of the external time-dependent field

With the help of the time-dependent gauge transformation technique, we have studied the geometric phase of a spin-half particle in a rotating magnetic field. We have found that the slow but finite frequency of the rotating magnetic field will make the difference between the adiabatic geometric phase and the exact geometric phase. When the frequency is much smaller than the energy space and the adiabatic condition is perfectly guaranteed, the adiabatic approximation geometric phase is exactly consistent with the adiabatic geometric phase. A simple relation for the accuracy of the adiabatic approximation is given in terms of the changing rate of the frequency of the rotating magnetic field and the energy level space.     

Phase-field study of the second phase particle effect on texture evolution of polycrystalline material

The second phase particle effect on texture evolution of polycrystalline material is studied through phase-field method. A unique field variable is introduced into the phase-field model to represent the second phase particles. Elastic interaction between particles and grains is also considered. Results indicate that in the presence of second phase particles the average particle diameter turns smaller than in the absence of these particles and retards texture formation by pinning effect. The second phase particles change the strain energy profile, which tremendously influences the pinning effect.     

Investigation of ultra—thin ferromagnetic films with a simple cubic lattice

Using Green‘s function method,we investigate ferromagnetic films with a simple cubic lattice containing up to ten monolayers.The Hamiltonian includes the Heisenberg exchange term,surface anisotropy (SA) and dipole interaction (DI).We calculate the magnetization as a function of temperature and film thickness,and we analyse the behaviour of spin canting.The result is in agreement with experiments.We calculate phase diagrams of SA versus DI to show the conditions under which spontaneous magnetization can occur.As a special case,we discuss the Heisenberg model without SA and DI.     

Interactions of a Projectile Charge with Two-Dimensional Dusty Plasmas

The interactions of a moving charge (namely, one additional dust particle) with a two-dimensional dusty plasma in gas discharge experiment are studied by means of the linearized hydrodynamic theory for the dusty plasma. Expressions are derived for the induced potential and the stopping power of the moving charge, when the charge flights parallel to and over the dust layer. The numerical results are obtained for different discharge pressures and different distances from the moving charge to the dust layer. The results show that the moving charge excites a V-shaped disturbance of induced potential or the so-called Mach cone in the dust layer, while the charge itself loses its energy.