161 research outputs found
On the theory of superfluidity
We investigate the properties of dispersion spectra of one-dimensional
periodic Bose systems with repulsive interparticle interactions. These systems
with sufficient large interactions can support metastable supercurrent states,
which correspond to the local minima of the dispersion spectra at non-zero
momenta. The existence of local minima in the spectra and the energy barriers,
which separate the minima, can be explained in terms of Bose exchange symmetry.
We extend our study to the case of higher dimensional Bose systems. We suggest
that superfluidity could be understood as a Bose exchange effect.Comment: simplified version; added references; 6 pages, 6 figure
The Spin Mass of an Electron Liquid
We show that in order to calculate correctly the {\it spin current} carried
by a quasiparticle in an electron liquid one must use an effective "spin mass"
, that is larger than both the band mass, , which determines the
charge current, and the quasiparticle effective mass , which determines
the heat capacity. We present microscopic calculations of in a
paramagnetic electron liquid in three and two dimensions, showing that the mass
enhancement can be a very significant effect.Comment: 10 pages, 1 figur
Structure change of Cooper pairs in color superconductivity -- Crossover from BCS to BEC ? --
We discuss a possibility of transition from color superconductivity of the
standard BCS type at high density, to Bose-Einstein Condensation (BEC) of
Cooper pairs at lower density. Examining two-flavor QCD over a wide range of
baryon density, we found the size of a Cooper pair becomes small enough to be
comparable to the averaged quark-quark distance at lower density. We also
consider the same problem in two-color QCD.Comment: 4pages, 2figures, Contribution to the Proceedings of "Quark Matter
2002", Nantes, France, 18-24 Jul 200
Spin-Hall effect in a [110] quantum well
A self-consistent treatment of the spin-Hall effect requires consideration of
the spin-orbit coupling and electron-impurity scattering on equal footing. This
is done here for the experimentally relevant case of a [110] GaAs quantum well
[Sih {\it et al.}, Nature Physics 1, 31 (2005)]. Working within the framework
of the exact linear response formalism we calculate the spin-Hall conductivity
including the Dresselhaus linear and cubic terms in the band structure, as well
as the electron-impurity scattering and electron-electron interaction to all
orders. We show that the spin-Hall conductivity naturally separates into two
contributions, skew-scattering and side-jump, and we propose an experiment to
distinguish between them.Comment: The connection with the recent experiment on [110] quantum wells is
emphasize
Kondo effect and channel mixing in oscillating molecules
We investigate the electronic transport through a molecule in the Kondo
regime. The tunneling between the electrode and the molecule is asymmetrically
modulated by the oscillations of the molecule, i.e., if the molecule gets
closer to one of the electrodes the tunneling to that electrode will increase
while for the other electrode it will decrease. The system is described by a
two-channel Anderson model with phonon-assisted hybridization, which is solved
with the Wilson numerical renormalization group method. The results for several
functional forms of tunneling modulation are presented. For a linearized
modulation the Kondo screening of the molecular spin is caused by the even or
odd conduction channel. At the critical value of the electron-phonon coupling
an unstable two-channel Kondo fixed point is found. For a realistic modulation
the spin at the molecular orbital is Kondo screened by the even conduction
channel even in the regime of strong coupling. A universal consequence of the
electron-phonon coupling is the softening of the phonon mode and the related
instability to perturbations that break the left-right symmetry. When the
frequency of oscillations decreases below the magnitude of such perturbation,
the molecule is abruptly attracted to one of the electrodes. In this regime,
the Kondo temperature is enhanced and, simultaneously, the conductance through
the molecule is suppressed.Comment: published versio
Charmonia above the Deconfinement Phase Transition
Analyzing correlation functions of charmonia at finite temperature () on
anisotropic lattices by the maximum entropy method (MEM),
we find that and survive as distinct resonances in the plasma
even up to and that they eventually dissociate between and ( is the critical temperature of deconfinement). This
suggests that the deconfined plasma is non-perturbative enough to hold
heavy-quark bound states. The importance of having sufficient number of
temporal data points in the MEM analysis is also emphasized.Comment: Lattice2003(nonzero), 3 pages, 3 figure
On-top fragmentation stabilizes atom-rich attractive Bose-Einstein condensates
It is well known that attractive condensates do not posses a stable ground
state in three dimensions. The widely used Gross-Pitaevskii theory predicts the
existence of metastable states up to some critical number
of atoms. It is demonstrated here that
fragmented metastable states exist for atom numbers well above
. The fragments are strongly overlapping in
space. The results are obtained and analyzed analytically as well as
numerically. The implications are discussed.Comment: 12 pages, 4 figure
Dynamics and scaling in the periodic Anderson model
The periodic Anderson model (PAM) captures the essential physics of heavy
fermion materials. Yet even for the paramagnetic metallic phase, a practicable
many-body theory that can simultaneously handle all energy scales while
respecting the dictates of Fermi liquid theory at low energies, and all
interaction strengths from the strongly correlated Kondo lattice through to
weak coupling, has remained quite elusive. Aspects of this problem are
considered in the present paper where a non-perturbative local moment approach
(LMA) to single-particle dynamics of the asymmetric PAM is developed within the
general framework of dynamical mean-field theory. All interaction strengths and
energy scales are encompassed, although our natural focus is the Kondo lattice
regime of essentially localized -spins but general conduction band filling,
characterised by an exponentially small lattice coherence scale .
Particular emphasis is given to the resultant universal scaling behaviour of
dynamics in the Kondo lattice regime as an entire function of , including its dependence on conduction band filling,
-level asymmetry and lattice type.A rich description arises, encompassing
both coherent Fermi liquid behaviour at low- and the crossover
to effective single-impurity scaling physics at higher energies -- but still in
the -scaling regime, and as such incompatible with the
presence of two-scale `exhaustion' physics, which is likewise discussed.Comment: 22 pages in EPJB format, 14 figures; accepted for publication in
EPJB; (small change in the comments section, no change in manuscript
Groundstates of SU(2)-Symmetric Confined Bose Gas: Trap for a Schr\"odinger Cat
Conservation of the total isotopic spin S of a two-component Bose gas-like
Rb-has a dramatic impact on the structure of the ground state. In the
case when S is much smaller than the total number of particles N, the
condensation of each of the two components occurs into two single-particle
modes. The quantum wavefunction of such a groundstate is a Schr\"odinger Cat-a
superposition of the phase separated classical condensates, the most "probable"
state in the superposition corresponding to the classical groundstate in the
sector of given N and S. After measurement of the spatial distribution of the
densities of the two components, the Cat collapses into one of the classical
condensate states.Comment: 5 RevTex pages, no figures; replaced with revised version, where the
discussion on stability against temporal white noise and losses is adde
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