Quantum Phases of Pancharatnam Type for a General Spin in a Time-Dependent Magnetic Field

Based on the quantum invariant theory,the quantum phases,including the total phase as well as its dynamical and geometric parts,of Pancharatnam type are derived for a general spin in a time-dependent magnetic field,without the constraint of adiabatic,cyclic or unitary condition.The geometric meaning of geometric phase is expounded.

Atomic Force Microscopy Studies of Barium Titanate Thin Films Prepared by Laser Molecular Beam Epitaxy

Laser molecular beam epitaxy(laser MBE)technique was utilized to grow the barium titanate(BaTiO_(3),BTO)thin films on SrTiO_(3)(100)substrates.The surface morphology of the BaTiO_(3) thin films was studied by atomic force microscopy(AFM).Two-and three-dimensional AFM images were obtained.The root mean square surface roughness,the height profile,the histogram and the bearing ratio of the height distributions for the BaTiO_(3) thin films were analyzed in detail.The results indicate that the laser MBE thin films exhibit an atomically smooth surface.

Structure and Transmission Spectra for Colloidal Crystals with Silica Spheres

An ordered colloidal structure of SiO_(2) spheres of 0.33μm diameter has been formed in distilled water.It is a face-centered cubic structure with a lattice constant of 0.54μm and a volume fraction of 0.48,as determined by the Kossel rings analysis.The light transmission in the[111]direction exhibited a dip located at 11600cm^(-1).A plane wave expansion method is used to calculate the lowest gap at the L point.The gap center coincides quite well with the measured transmission dip.

Synthesis and Characterization of Titanosilicate with the Structure of Umbite

A zeolitic titanosilicate with the composition of K_2TiSi_3O_9·H_2O, a structural analogue of natural mineral umbite K_2ZrSi_3O_9·H_2O, was hydrothermally synthesized in the SiO_2-TiO_2-K_2O-H_2O system and characterized by means of powder X-ray diffraction, SEM, IR and thermal analysis. The effects of TiO_2/SiO_2 and OH -/SiO_2 ratios on the crystallization of the umbite were discussed. The influence of the organic additives on the morphology of the crystal was also investigated and the crystals with different shapes were obtained.

Enhanced Photorefractive Properties of a Rh-Doped BaTiO_(3) Crystal at Elevated Temperature

Two-beam coupling and self-pumped phase conjugation properties of a Rh-doped BaTiO_(3) crystal were investigated at 633nm as the temperature was increased from 20 to 50℃.A significant decrease in response time and an increase in gain of two-beam coupling were obtained.The self-pumped phase conjugation reflectivity was increased from 45 to 64%in this temperature range.

Phase-Sensitive Detection of Raman-Enhanced Nondegenerate Four-Wave Mixing by Polarization Interference

We demonstrated a phase-sensitive method for studying the Raman-enhanced nondegenerate four-wave mixing(RENFWM).The reference beam is another four-wave mixing signal,which propagates along the same optical path as the RENFWM signal.This method is used for studying the phase dispersion of the third-ordersusceptibility X^((3))and for the optical heterodyne detection of the RENFWM signal.

Manifestation of Quantum Chaos in the Spectra of Quantum Well with Tilted Magnetic Field

Two statistical properties,the nearest neighbor energy level spacing distribution P(s)and the spectral rigidityΔ3(L),are reported for energy level of a quantum well in a tilted magnetic field.Time-reversal(T)symmetry is broken in the system.The system is invariant under the anti-unitary combination of symmetric operations which include T,leading to what is called false T-violation.With the increasing magnetic field,P(s)andΔ3(L)change from Brody type-like distribution to the Gaussian orthogonal ensemble(GOE)distribution.This result is a clear manifestation of quantum chaos in the system and is in agreement with the prediction of which the false T-violation suffices to give the energy spectra the properties of the GOE,instead of the Gaussian unitary ensemble(GUE).The result indicates that the system translates from mixed-type state to quantum chaotic state.However,the spectral rigidityΔ3(L)turns into GUE with the magnetic field increasing.The different demonstration of P(s)and theΔ3(L)is due to the counting of only finite semi-classical orbits.

High-Order Harmonic Generation in the Presence of Static Electric Field

We study the effects of the static electric field on the high-order harmonic generation(HOHG).It is found that the presence of the static electric field breaks the inversion and reflection symmetry,as a result,the HOHG spectrum exhibits a double plateau structure.Furthermore,the cutoff of the HOHG is no longer corresponding to the maximum kinetic energy the ionized electron can obtain from the laser field.Instead,it corresponds to the maximum kinetic energy of the electron with one return.

Hysteresis Loop of Energy Transfer in Two-Wave Mixing from 180° Domains in BaTiO_(3):Ce

This paper reports an experimental observation that a hysteresis loop of energy transfer versus an external electric field is obtained in photorefractive two-wave mixing,which originates from 180°domains presented in the crystal.

Eigenvalues and Eigenfunctions of a Stadium-Shaped Quantum Dot Subjected to a Perpendicular Magnetic Field

The eigenvalues and eigenfunctions of the stadium-shaped quantum dot subjected to a constant magnetic field in the perpendicular direction are computed by a simple and efficient method.With the magnetic field increasing,the nearest-neighour-energy-level-spacing distribution of the stadium-shaped quantum dot is found to transform gradually from the Wigner distribution to the Poisson distribution.The transition of the nearest-neighour-energy-level-spacing distribution indicates that system changes from quantum chaotic to regular.The variation of the spatial charge distribution indicates that the system varies from bulk Landau state to the edge state that mainly affects the transport properties of the stadium-shaped quantum dot.The change of the two dimensional charge distribution near the anticrossing point is also discussed.

Photorefractive Image Amplification and Beam Fanning with Inclusion of Random Volume Scattering

Photorefractive effects,such as the image amplification and the beam fanning,can be described by a set of multivariable Langevin equations with inclusion of the random-phased volume scattering due to the inhomogeneities and/or defects in the crystal.The image amplification by two-wave-coupling configuration was studied analytically in the undepleted-pump approximation and numerically.It was found that the volume scattering can generate the beam fanning,as the surface scattering does.

Transport Properties of Ferromagnet/Ferromagnetic-Insulator/Ferromagnet Junctions Attached by a Paramagnetic Metal on Two Sides

The electronic-transport properties of ferromagnet/ferromagnetic-insulator/ferromagnet junctions attached on two sides by a paramagnetic metal are analyzed.The tunnel conductance and magnetoresistance are oscillatory functions of the ferromagnet thickness.The exchange coupling between ferromagnets depends on both the magnetic polarization of the conduction electrons and the exchange splitting in all the magnetic layers.

Effect of the Transition Sublayers at the Interfaces on Giant Magnetoresistance

A thin transition sublayer between the ferromagnetic and the nonmagnetic sublayers is introduced for describing the interface roughness and/or the interface alloying.Based on the Kubo formalism in the real spaces,the giant magnetoresistance effects for both the cases of the structures with and without the transition sublayers at the interfaces are discussed.The numerical results show that the transition sublayers induce a phase shift on the curves of magnetoresistance(MR)vs the thicknesses of the ferromagnetic and the nonmagnetic sublayers,and there exists a critical thickness dc of the ferromagnetic sublayer,the ratio of the MR values for the structures with and without the transition sublayers at the interfaces changes at the critical thickness.

Asymmetrical Spin-Polarized Tunneling in a Composed-Barrier Magnetic Tunnel Junctions Under the Forward and Reverse Biases

Based on the two-band model and nearly-free-electron approximation, the tunnel current, conductance and mag-netoresistance of the composed-barrier magnetic tunnel junctions ( MTJ ) under the forward and reverse biases are discussed, respectively, and the numerical results are compared with the experimental results of the single-barrier MTJ . We find that there exists an asymmetrical spin-polarized tunneling in this structure under the forward and reverse biases. It suggests that this type of MTJ will provide novel functions to the potential applications of traditional types of MTJ.

Growth Mode of Superconducting La_(2-x)Sr_(x)Cu_(l+y)O_(4) Thin Films on LaAlO_(3) Substrate

La_(2-x)Sr_(x)Cu_(l+y)O_(4)(LSCO)thin films sputtered from a Cu-rich target on a LaAlO_(3) substrate showed a columnar structure.The columnar grains penetrated the full thickness of the film,nucleating at the substrate surface defects.Transmission electron microscopy revealed two kinds of lattice images:one with a lattice spacing of 0.66 nm and the other with a spacing of 0.61 nm.The 0.66 nm spacing denotes a c-axis oriented LSCO film matrix.The 0.61 nm spacing has two categories:one with short white dashes,the phase of which is not yet identified,the other with no additional structure,which could correspond to the c-axis deviated LSCO.

Nonlinear Optical Properties of Some New Conjugated Copolymers

The ground-and the excited-state nonlinearities of two new copolymers are investigated in nanosecond scale at 1064 nm.It is found that the excited-state susceptibility is dramatically larger than the corresponding ground-state susceptibility for each sample.The experimental results also give evidence that superlattice structure of the copolymers can enhance,especially for the excited state,the molecular hyperpolarizabilities significantly.This enhancement may be attributed to the confinement effect of the pump-induced carriers.

Microstructure and Magnetization Investigations of Cu-Doping Effect on La_(2)CuO_(4+δ) Crystal

Measurement and characterization were carried out on Cu-doped and undoped La_(2)CuO_(4+δ) samples prepared under the same conditions.The magnetization measurement on the Cu-doped La_(2)CuO_(4+δ) sample shows coexistence of long-range antiferromagnetic order and superconductivity.A stripe-like structure was observed at room temperature on the ab-plane of Cu-doped La_(2)CuO_(4+δ) sample by transmission electron microscope.While for the undoped La_(2)CuO_(4+δ) sample no such behavior or structure feature was found.In this letter,these phenomena were discussed in terms of phase separation.

Mössbauer Spectroscopy and X-Ray Diffraction Studies of the Phase Composition of Crystallized Nd_(x)Fe_(81.5-x)B_(18.5) Alloys with 7 ≤ x ≤15

The phase composition of melt-spun Nd-Fe-B with intermediate and high Nd concentrations has been studied by Mössbauer effect.Based on the knowledge of the ^(57)Fe hyperfine parameters for Nd_(2)Fe_(14)B,Nd_(2)Fe_(23)B_(3),and Nd_(1.1)Fe_(4)B_(4),the phases produced during annealing Nd-Fe-B amorphous alloys can be identified.It is found that the Nd_(x)Fe_(81.5-x)B_(18.5) samples with 7≤x≤9 contain the Nd_(2)Fe_(23)B_(3) metastable phase and the Nd1.1Fe4B4 paramagnetic phase.The body-centered-cubic structure of Nd_(2)Fe_(23)B_(3) cannot generate the hard magnetic properties.The samples with 12≤x≤15 consist of the Nd_(2)Fe_(14)B hard magnetic phase and the Nd1.1Fe4B4 paramagnetic phase.The large coercivity for the high Nd content Nd-Fe-B originates from the very fine size of Nd_(2)Fe_(14)B grains below the particle size of the single domain,which may contribute to a pinning effect of domain wall.

Synchrotron X-Ray Study on Structures of Ni_(80)Fe_(20)/Cu Superlattices

We showed that,in contrast to the results in literature,the Bragg peak intensity of Ni_(80)Fe_(20)/Cu superlattices is enhanced at the incident x-ray energy slightly higher than the absorption edge of the heavier element(Cu).The atomic density at Ni_(80)Fe_(20)/Cu interface was analysed by the diffraction anomalous fine structure technology with the incident angle of x-ray fixed at the first Bragg peak.Our results demonstrate the epitaxy growth of Ni_(80)Fe_(20)/Cu superlattices.Upon annealing,the epitaxity of Ni_(80)Fe_(20)/Cu multilayers becomes poor but the local crystallinity in each layer is improved.

Formal Scattering Approach to High-Order Harmonic Generation

By using the time-independent formal scattering theoretical approach,we develop a nonperturbative quantum electrodynamics theory to describe high-order harmonic generation(HHG).This theory recovers the semi-classical interpretation of Corkum(Phys.Rev.Lett.71(1993)1994)and gives the same phenomenological cutoff law.The HHG emission rate is expressed as an analytic closed form.We also discuss the connection between HHG and the above threshold ionization from the scattering viewpoint.