Rapidly rotating Bose-Einstein condensates in an anharmonic confinement

We examine a rapidly rotating Bose-Einstein condensate in an anharmonic confinement and find that many properties such as the critical rotating frequency and phase diagram are quite different from those in a harmonic trap. We investigate the phase transitions by means of average-vortex-approximation. We find that the vortex lattice consists of a vortex array with a hole in the center of the cloud as the rotating frequency $\Omega$ increases and the vortex becomes invisible when $\Omega$ reaches some value.Comment: Revtex, 5 pages, 2 figure

Microscopic Study of Slablike and Rodlike Nuclei: Quantum Molecular Dynamics Approach

Structure of cold dense matter at subnuclear densities is investigated by quantum molecular dynamics (QMD) simulations. We succeeded in showing that the phases with slab-like and rod-like nuclei etc. can be formed dynamically from hot uniform nuclear matter without any assumptions on nuclear shape. We also observe intermediate phases, which has complicated nuclear shapes. Geometrical structures of matter are analyzed with Minkowski functionals, and it is found out that intermediate phases can be characterized as ones with negative Euler characteristic. Our result suggests the existence of these kinds of phases in addition to the simple ``pasta'' phases in neutron star crusts.Comment: 6 pages, 4 figures, RevTex4; to be published in Phys. Rev. C Rapid Communication (accepted version

Landau theory of phase separation in cuprates

I discuss the problem of phase separation in cuprates from the point of view of the Landau theory of Fermi liquids. I calculate the rate of growth of unstable regions for the hydrodymanics and collisionless limit and, in presence of long range Coulomb interactions, the size of these regions. These are analytic results valid for any strength of the Landau parameters.Comment: RevteX, preprint ITP (1994

Critical points in a relativistic bosonic gas induced by the quantum structure of spacetime

It is well known that phase transitions arise if the interaction among particles embodies an attractive as well as a repulsive contribution. In this work it will be shown that the breakdown of Lorentz symmetry, characterized through a deformation in the relation dispersion, plus the bosonic statistics predict the emergence of critical points. In other words, in some quantum gravity models the structure of spacetime implies the emergence of critical points even when no interaction among the particle has been considered.Comment: 5 pages, no figure

Feshbach Resonances and Medium Effects in ultracold atomic Gases

We develop an effective low energy theory for multi-channel scattering of cold atomic alkali atoms with particular focus on Feshbach resonances. The scattering matrix is expressed in terms of observables only and the theory allows for the inclusion of many-body effects both in the open and in the closed channels. We then consider the frequency and damping of collective modes for Fermi gases and demonstrate how medium effects significantly increase the scattering rate determining the nature of the modes. Our results obtained with no fitting parameters are shown to compare well with experimental data.Comment: Presented at the 5th workshop on Critical Stability, Erice, Italy 13-17 October 2008. 8 pages, 3 figures. Figure caption correcte

A possible cooling effect in high temperature superconductors

We show that an adiabatic increase of the supercurrent along a superconductor with lines of nodes of the order parameter on the Fermi surface can result in a cooling effect. The maximum cooling occurs if the supercurrent increases up to its critical value. The effect can also be observed in a mixed state of a bulk sample. An estimate of the energy dissipation shows that substantial cooling can be performed during a reasonable time even in the microkelvin regime.Comment: 5 pages, to appear in Phys. Rev.

Self-consistent calculation of the coupling constant in the Gross-Pitaevskii equation

A method is proposed for a self-consistent evaluation of the coupling constant in the Gross-Pitaevskii equation without involving a pseudopotential replacement. A renormalization of the coupling constant occurs due to medium effects and the trapping potential, e.g. in quasi-1D or quasi-2D systems. It is shown that a simplified version of the Hartree-Fock-Bogoliubov approximation leads to a variational problem for both the condensate and a two-body wave function describing the behaviour of a pair of bosons in the Bose-Einstein condensate. The resulting coupled equations are free of unphysical divergences. Particular cases of this scheme that admit analytical estimations are considered and compared to the literature. In addition to the well-known cases of low-dimensional trapping, cross-over regimes can be studied. The values of the kinetic, interaction, external, and release energies in low dimensions are also evaluated and contributions due to short-range correlations are found to be substantial.Comment: 15 pages, ReVTEX, no figure

Weakly-Interacting Bosons in a Trap within Approximate Second Quantization Approach

The theory of Bogoliubov is generalized for the case of a weakly-interacting Bose-gas in harmonic trap. A set of nonlinear matrix equations is obtained to make the diagonalization of Hamiltonian possible. Its perturbative solution is used for the calculation of the energy and the condensate fraction of the model system to show the applicability of the method.Comment: 6 pages, two figures .Presented at the International Symposium on Quantum Fluids and Solids QFS2006 (Kyoto, Japan

Self-consistent scattering description of transport in normal-superconductor structures

We present a scattering description of transport in several normal-superconductor structures. We show that the related requirements of self-consistency and current conservation introduce qualitative changes in the transport behavior when the current in the superconductor is not negligible. The energy thresholds for quasiparticle propagation in the superconductor are sensitive to the existence of condensate flow ($v_s\neq 0$). This dependence is responsible for a rich variety of transport regimes, including a voltage range in which only Andreev transmission is possible at the interfaces, and a state of gapless superconductivity which may survive up to high voltages if temperature is low. The two main effects of current conservation are a shift towards lower voltages of the first peak in the differential conductance and an enhancement of current caused by the greater availability of charge transmitting scattering channels.Comment: 31 pages, 10 PS figures, Latex file, psfig.sty file is added. To appear in Phys. Rev. B (Jan 97

On phases in weakly interacting finite Bose systems

We study precursors of thermal phase transitions in finite systems of interacting Bose gases. For weakly repulsive interactions there is a phase transition to the one-vortex state. The distribution of zeros of the partition function indicates that this transition is first order, and the precursors of the phase transition are already displayed in systems of a few dozen bosons. Systems of this size do not exhibit new phases as more vortices are added to the system.Comment: 7 pages, 2 figure