Critical Scaling of Extended Power Law I - V Isotherms near Vortex Glass Transition

In view of the question about the vortex glass theory of the freezing of disordered vortex matter raised by recent experimental observations, we reinvestigate the critical scaling of high Tc superconductors. It is found that the dc current-voltage characteristic of mixed state superconductors has a general form of extended power law which is based on the Ginzburg-Landau （GL） functional in the similar way as the vortex glass theory. Isotherms simulated from this nonlinear equation fit the experimental I- V data of Strachan et al. [Phys. Rev. Left. 87（2001） 067007]. The puzzling question of the derivative plot for the I - V curves and the controversy surrounding the values of critical exponents are discussed.     

利用单轴压强下的电阻变化研究铁基超导体中的向列涨落

铁基超导体中普遍存在着反铁磁、超导和向列相,因此研究向列相的性质及其与反铁磁、超导的关系对于理解铁基超导体的低能物理及高温超导电性具有非常重要的作用.所谓向列相是指电子态自发破缺了晶格的面内四重旋转对称性而形成的有序态,从而导致样品的某些物理性质出现了两重的各向异性.我们通过自主研发的单轴压强装置,可以在低温下原位改变压强,测量电阻的变化,从而得到向列极化率.本文介绍了我们利用该装置在最近几年研究铁基超导体的向列相和向列涨落所取得的一些成果,包括详细研究了BaFe_(2-x)Ni_xAs_2体系中的向列量子临界点及其量子临界涨落,并提出了基于向列涨落强弱调节的铁基超导体统一相图.这些结果表明,向列相及其涨落与反铁磁和超导均有很强的耦合,对于理解铁基超导体中磁性和超导电性非常关键.     

Anomalous Hall conductivity from the dipole mode of spin-orbit-coupled cold-atom systems

Motivated by recent experiments by Lin et al., [Nature (London) 471, 83 (2011)] that engineered spin-orbit coupling in ultracold mixtures of bosonic atoms, we study the dipole oscillation of trapped spin-orbit-coupled noncondensed Bose and Fermi gases. We find that different directions of oscillation are coupled by the spin-orbit interactions. The phase difference between oscillatory motion in orthogonal directions and the trapping frequencies of the modes are shown to be related to the anomalous Hall conductivity. Our results can be used to experimentally determine the anomalous Hall conductivity for cold-atom systems.     

Transport behaviour of a Bose Einstein condensate in a bichromatic optical lattice

We investigate the Bloch and dipole oscillations of a Bose Einstein condensate (BEC) in an optical superlattice. We show that, as the effective mass increases in an optical superlattice, the BEC is localized in accordance with recent experimental observations [J.E. Lye et. al. Phys. Rev. A 75, 061603 (2007)]. In addition, we find that the secondary optical lattice is a useful additional tool to manipulate the dynamics of the atoms.      

Photon condensation: A new paradigm for Bose–Einstein condensation

Bose–Einstein condensation is a state of matter known to be responsible for peculiar properties exhibited by superfluid Helium-4 and superconductors. Bose–Einstein condensate (BEC) in its pure form is realizable with alkali atoms under ultra-cold temperatures. In this paper, we review the experimental scheme that demonstrates the atomic Bose–Einstein condensate. We also elaborate on the theoretical framework for atomic Bose–Einstein condensation, which includes statistical mechanics and the Gross–Pitaevskii equation. As an extension, we discuss Bose–Einstein condensation of photons realized in a fluorescent dye filled optical microcavity. We analyze this phenomenon based on the generalized Planck’s law in statistical mechanics. Further, a comparison is made between photon condensate and laser. We describe how photon condensate may be a possible alternative for lasers since it does not require an energy consuming population inversion process.     

Magnetic ordering in Ce2RhSi3

The results of magnetic susceptibility, heat-capacity, electrical resistivity and magnetoresistance measurements on the compound Ce₂RhSi₃ prove that this alloy orders antiferromagnetically at 6 K in support of an original report by Chevalier et al. [Solid State Commun. 49 (1984) 753] but in contrast to the conclusions from neutron diffraction results [Szytula et al., J. Magn. Magn. Mater. 118 (1993) 302].     

Superconductivity as a consequence of an ordering of the electron gas zero-point oscillations

It is shown that the temperature dependence of the value of energy gap in superconductors is characteristic for the order–disorder transition. The obtained relationship between the critical parameters of the Bose–Einstein condensate of electrically charged particles is in accordance with measurement data of superconductor critical parameters. The dependence of the critical temperatures for both – I and II – type superconductors and their Sommerfeld constants (and their Fermi energies) is obtained. It is marked that among the high-temperature superconducting ceramics there are the both – I and II – type superconductors. In total the phenomenon of superconductivity is seen as a consequence of ordering into the zero-point oscillation system of the electron gas in a metal at low temperatures. The obtained estimations of the interaction of zero-point oscillations are in satisfactory agreement with the data measurements of critical parameters of I and II type superconductors.     

Low-temperature thermal conductivity of superconductors with gap nodes

We report a detailed analytic and numerical study of electronic thermal conductivity in d-wave superconductors. We compare theory of the crossover at low temperatures from T dependence to T(3) dependence for increasing temperature with recent experiments on YBa(2)Cu(3)O(7) in zero magnetic field for T approximately [0.04 K,0.4 K] by Hill et al. [Phys. Rev. Lett. 92, 027001 (2004)]. Transport theory, including impurity scattering and inelastic scattering within strong-coupling superconductivity, can consistently fit the temperature dependence of the data in the lower half of the temperature regime. We discuss the conditions under which we expect power-law dependences over wide temperature intervals.     

Structural relaxation and aging scaling in the Coulomb and Bose glass models

We employ Monte Carlo simulations to study the relaxation properties of the two-dimensional Coulomb glass in disordered semiconductors and the three-dimensional Bose glass in type-II superconductors in the presence of extended linear defects. We investigate the effects of adding non-zero random on-site energies from different distributions on the properties of the correlation-induced Coulomb gap in the density of states (DOS) and on the non-equilibrium aging kinetics highlighted by the density autocorrelation functions. We also probe the sensitivity of the system’s equilibrium and non-equilibrium relaxation properties to instantaneous changes in the density of charge carriers in the Coulomb glass or flux lines in the Bose glass.     

Analytical approach to quantum phase transitions of ultracold Bose gases in bipartite optical lattices using the generalized Green’s function method

In order to investigate the quantum phase transitions and the time-of-flight absorption pictures analytically in a systematic way for ultracold Bose gases in bipartite optical lattices, we present a generalized Green’s function method. Utilizing this method, we study the quantum phase transitions of ultracold Bose gases in two types of bipartite optical lattices, i.e., a hexagonal lattice with normal Bose–Hubbard interaction and a d-dimensional hypercubic optical lattice with extended Bose–Hubbard interaction. Furthermore, the time-of-flight absorption pictures of ultracold Bose gases in these two types of lattices are also calculated analytically. In hexagonal lattice, the time-of-flight interference patterns of ultracold Bose gases obtained by our analytical method are in good qualitative agreement with the experimental results of Soltan-Panahi, et al. [Nat. Phys. 7, 434 (2011)]. In square optical lattice, the emergence of peaks at \(\left( { \pm \frac{\pi }{a}, \pm \frac{\pi }{a}} \right)\) in the time-of-flight absorption pictures, which is believed to be a sort of evidence of the existence of a supersolid phase, is clearly seen when the system enters the compressible phase from charge-density-wave phase.     

High pressure study on the superconducting transition temperature and Hall coefficient of Ba1−xKxBiO3 up to 8 GPa

The superconducting transition temperature (T_c) of Ba_0.62K_0.38Bio₃ (T_c=30 K) has been measured under high pressure up to 8 GPa. It is observed that T_c increases initially with pressure, as reported by Uwe et al., Shirber et al. and Huang et al., but decreases above 4 GPa. The Hall coefficient of Ba_0.62K_0.38BiO₃ has been measured up to 1.2 GPa. The absolute value of the Hall coefficient decreases with pressure by 10% GPa, the value of which is almost the same as that obtained in most CuO-based high-temperature superconductors.     

Optical and dc conductivities in high-T c superconductors: Spin-fluctuation scattering in the Emery model

On the basis of the Emery model for the CuO₂ plane, the optical conductivity and resistivity due to the inelastic scattering of oxygen holes by antiferromagnetic fluctuations of copper spins are calculated. For moderate hole doping, the electrical conductivity obeys a generalized Drude law. Using a phenomenological model for the dynamic spin susceptibility, the in-plane resistivity reveals a crossover from a quadratic to a linear temperature dependence at the scale of the spin-fluctuation energy. The frequency dependence of the scattering rate changes from a quadratic to a linear increase over a wide frequency range. The theory is compared with experiments on LSCO and YBCO compounds, where the spin dynamics is described within the model by Millis et al. A good quantitative agreement (in particular of the frequency-dependent scattering rate) with experiments is found. We conclude that the spin-fluctuation scattering may play a dominant role in the transport properties of Cu-oxide superconductors.     

Comments on "Intraspecific and geographic variation of West Indian manatee (Trichechus manatus spp.) vocalizations" [J. Acoust. Soc. Am. 114, 66-69 (2003)

This letter concerns the paper "Intraspecific and geographic variation of West Indian manatee (Trichechus manatus spp.) vocalizations" [Nowacek et al., J. Acoust. Soc. Am. 114, 66-69 (2003)]. The purpose here is to correct the fundamental frequency range and information on intraindividual variation in the vocalizations of Amazonian manatees reported by Nowacek et al. (2003) in citing the paper "Signature information and individual recognition in the isolation calls of Amazonian manatees, Trichechus inunguis (Mammalia: Sirenia)" [Sousa-Lima et al., Anim. Behav. 63, 301-310 (2002)].     

Collisions of solitons and vortex rings in cylindrical Bose-Einstein condensates

Interactions of solitary waves in a cylindrically confined Bose-Einstein condensate are investigated by simulating their head-on collisions. Slow vortex rings and fast solitons are found to collide elastically contrary to the situation in the three-dimensional homogeneous Bose gas. Strongly inelastic collisions are absent for low density condensates but occur at higher densities for intermediate velocities. The scattering behavior is rationalized by use of dispersion diagrams. During inelastic collisions, spherical shell-like structures of low density are formed and they eventually decay into depletion droplets with solitary-wave features. The relation to similar shells observed in a recent experiment by Ginsberg et al. [Phys. Rev. Lett. 94, 040403 (2005)] is discussed.     

Possible exciton bose liquid in a hard-core boson ring model

We present a quantum Monte?Carlo study of a hard-core boson model with ring-only exchanges on a square lattice, where a K1 term acts on 1×1 plaquettes and a K2 term acts on 1×2 and 2×1 plaquettes. At half-filling, the phase diagram reveals charge density wave for small K2, valence bond solid for intermediate K2, and possibly for large K2 the novel exciton Bose liquid (EBL) phase first proposed by Paramekanti et?al [Phys. Rev. B 66, 054526 (2002)10.1103/PhysRevB.66.054526]. Away from half-filling, the EBL phase is present already for intermediate K2 and remains stable for a range of densities below 1/2 before phase separation sets in at lower densities.     

Helium-4 Bose fluids formed in one-dimensional 18 A diameter pores

Bose fluids restricted in one dimension (1D) are realized by adsorbing 4He atoms on the 1D pore walls with a diameter of about 18 A. The Bose fluid appears above an adsorbed amount after the pore walls are coated with the inert 4He atoms. Heat capacity of the fluid was observed to have a temperature-linear term at low temperatures. This corresponds to the phonon heat capacity of the Bose fluid in the 1D pores. We estimate the phonon velocity and the interaction of the 1D Bose fluid.     

Properties of a two-dimensional semimetal in a strong magnetic field

A system of two-dimensional electrons and holes ha s been investigated in a strong magnetic field, when it is sufficient to take into account only the ground Landau level. It has been shown that the interaction of electrons and holes can lead to an ordered state. In this problem, the exchange interaction in electron and hole subsystems is significant. The following two cases have been considered: (a) there are one electron and one hole valleys, and at some magnetic field strength, there exists an ordered state, as in an excitonic insulator; and (b) there exist one electron and two equivalent hole valleys (as in the experiment performed by Kvon et al. [1]), and the hole system has an ordered state of the Stoner ferromagnetic type in a specific range of magnetic field strengths. The spectra of elementary excitations of the Bose and Fermi types have been obtained. The Fermi excitations have a gap in the energy spectrum, whereas the Bose excitations in the ordered states begin with zero (to these excitations there corresponds an electric dipole moment). The self-consistent field approximation has been used, which is exact when the numbers of electrons and holes are equal to each other.     

Comment on "Optical-fiber-based Mueller optical coherence tomography"

We comment on the recent Letter by Jiao et al. [Opt. Lett. 28, 1206 (2003)] in which a polarization-sensitive optical coherence tomography system was presented. Interrogating a sample with two orthogonal incident polarization states cannot always recover birefringence correctly. A previously presented fiber-based polarization-sensitive system was inaccurately characterized, and its method of eliminating the polarization distortion caused by single-mode optical fiber was presented earlier by Saxer et al. [Opt. Lett. 25, 1355 (2000)].     

Comment: On charged analogue of shear-free fluids

Recently, Gupta et al. [2] claim that solutions with NDG have no uncharged analogue. This claim seems to be partially correct as it is seen in present article that neutral shear-free fluid (f =α₁ x ^−5/2α₁ being a constant) given by Stephani [3] can be charged.     

Local-field correction of the charged Bose condensate for two and three dimensions

The local-field correction for the dielectric function of the two-dimensional and of the three-dimensional Bose condensate is calculated within a sum-rule version of the Singwi et al. (Phys. Rev.176, 589 (1968)) approach. We derive analytical expressions for small and large wave numbers and give analytical expressions for the density dependence. We compare the results of the groundstate energy for the three-dimensional system with Monte-Carlo computations. In two dimensions a roton structure in the plasmon dispersion is found at low boson density. The plasmon density of states is calculated. A correlation induced charge-density-wave instability in layered structures of two-dimensional Bose gases is discussed.