2,438 research outputs found
Sound modes at the BCS-BEC crossover
First and second sound speeds are calculated for a uniform superfluid gas of
fermi atoms as a function of temperature, density and interaction strength. The
second sound speed is of particular interest as it is a clear signal of a
superfluid component and it determines the critical temperature. The sound
modes and their dependence on density, scattering length and temperature are
calculated in the BCS, molecular BEC and unitarity limits and a smooth
crossover is extrapolated. It is found that first and second sound undergo
avoided crossing on the BEC side due to mixing. Consequently, they are
detectable at crossover both as density and thermal waves in traps.Comment: To appear in Phys. Rev.
Singlet and triplet BCS pairs in a gas of two-species fermionic polar molecules
We investigate the BCS pairing in a mixture of fermionic polar molecules with
two different hyperfine states. We derive a set of coupled gap equations and
find that this system supports both spin-singlet and -triplet BCS pairs. We
also calculate the critical temperatures and the angular dependence of order
parameters. In addition, by tuning short-range interaction between
inter-species molecules, the transition between singlet and triplet paired
states may be realized.Comment: 5 pages, 4 figure
Thermodynamically consistent equilibrium properties of normal-liquid Helium-3
The high-precision data for the specific heat C_{V}(T,V) of normal-liquid
Helium-3 obtained by Greywall, taken together with the molar volume V(T_0,P) at
one temperature T_0, are shown to contain the complete thermodynamic
information about this phase in zero magnetic field. This enables us to
calculate the T and P dependence of all equilibrium properties of normal-liquid
Helium-3 in a thermodynamically consistent way for a wide range of parameters.
The results for the entropy S(T,P), specific heat at constant pressure
C_P(T,P), molar volume V(T,P), compressibility kappa(T,P), and thermal
expansion coefficient alpha(T,P) are collected in the form of figures and
tables. This provides the first complete set of thermodynamically consistent
values of the equilibrium quantities of normal-liquid Helium-3. We find, for
example, that alpha(T,P) has a surprisingly intricate pressure dependence at
low temperatures, and that the curves alpha(T,P) vs T do not cross at one
single temperature for all pressures, in contrast to the curves presented in
the comprehensive survey of helium by Wilks.
Corrected in cond-mat/9906222v3: The sign of the coefficient d_0 was
misprinted in Table I of cond-mat/9906222v1 and v2. It now correctly reads
d_0=-7.1613436. All results in the paper were obtained with the correct value
of d_0. (We would like to thank for E. Collin, H. Godfrin, and Y. Bunkov for
finding this misprint.)Comment: 19 pages, 19 figures, 9 tables; published version; note added in
proof; v3: misprint correcte
Paired phases and Bose-Einstein condensation of spin-one bosons with attractive interaction
We analyze paired phases of cold bosonic atoms with the hyper spin S=1 and
with an attractive interaction. We derive mean-field self-consistent equations
for the matrix order parameter describing such paired bosons on an optical
lattice. The possible solutions are classified according to their symmetries.
In particular, we find that the self-consistent equations for the SO(3)
symmetric phase are of the same form as those for the scalar bosons with the
attractive interaction. This singlet phase may exhibit either the BCS type
pairing instability (BCS phase) or the BEC quasiparticle condensation together
with the BCS type pairing (BEC phase) for an arbitrary attraction U_0 in the
singlet channel of the two body interaction. We show that both condensate
phases become stable if a repulsion U_2 in the quintet channel is above a
critical value, which depends on U_0 and other thermodynamic parameters.Comment: 9 pages, 4 figure
Segmented Band Mechanism for Itinerant Ferromagnetism
We introduce a novel mechanism for itinerant ferromagnetism, which is based
on a simple two-band model, and using numerical and analytical methods, we show
that the Periodic Anderson Model (PAM) contains this mechanism. We propose that
the mechanism, which does not assume an intra-atomic Hund's coupling, is
present in both the iron group and some electron compounds
Magnetic properties of the Anderson model: a local moment approach
We develop a local moment approach to static properties of the symmetric
Anderson model in the presence of a magnetic field, focussing in particular on
the strong coupling Kondo regime. The approach is innately simple and
physically transparent; but is found to give good agreement, for essentially
all field strengths, with exact results for the Wilson ratio, impurity
magnetization, spin susceptibility and related properties.Comment: 7 pages, 3 postscript figues. Latex 2e using the epl.cls Europhysics
Letters macro packag
Effects of the Nearest-Neighbour Coulomb Interactions on the Ground State of the Periodic Anderson Model
The magnetic and non-magnetic ground states of the periodic Anderson model
with Coulomb interaction between -electrons on the nearest-neighbour(NN)
sites are investigated using a variational method, which gives exact
calculation of the expectation values in the limit of infinite dimensions. It
is shown that for a critical value of NN Coulomb interactions the magnetic
ground state of the periodic Anderson model in the Kondo regime is unstable.
Factors in terms of the physical processes responsible for instability of the
magnetic ground state are also discussed. Our study indicates the importance of
the NN Coulomb interactions for correlated two band models.Comment: RevTeX, 6 pages, 5 figures, to appear in Phys. Rev.
Dynamic generation of spin orbit coupling
Spin-orbit coupling plays an important role in determining the properties of
solids, and is crucial for spintronics device applications. Conventional
spin-orbit coupling arises microscopically from relativistic effects described
by the Dirac equation, and is described as a single particle band effect. In
this work, we propose a new mechanism in which spin-orbit coupling can be
generated dynamically in strongly correlated, non-relativistic systems as the
result of fermi surface instabilities in higher angular momentum channels.
Various known forms of spin-orbit couplings can emerge in these new phases, and
their magnitudes can be continuously tuned by temperature or other quantum
parameters.Comment: Accepted by Phys. Rev. Lett., 4 pages, 1 figur
Creation of Skyrmions in a Spinor Bose-Einstein Condensate
We propose a scheme for the creation of skyrmions (coreless vortices) in a
Bose-Einstein condensate with hyperfine spin F=1. In this scheme, four
traveling-wave laser beams, with Gaussian or Laguerre-Gaussian transverse
profiles, induce Raman transitions with an anomalous dependence on the laser
polarization, thereby generating the optical potential required for producing
skyrmions.Comment: 5 pages, 2 figures, RevTe
Shear viscosity of the A_1-phase of superfluid 3He
The scattering processes between the quasiparticles in spin- up superfluid
with the quasiparticles in spin-down normal fluid are added to the other
relevant scattering processes in the Boltzmann collision terms. The Boltzmann
equation has been solved exactly for temperatures just below T_c_1. The shear
viscosity component of the A_1- phase drops as C_1(1-T/T_c_1)^(1/2). The
numerical factor C_1 is in fairly good agreement with the experiments
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