7,536 research outputs found
Fermi-liquid effects in the Fulde-Ferrell-Larkin-Ovchinnikov state of two-dimensional d-wave superconductors
We study the effects of Fermi-liquid interactions on quasi-two-dimensional
d-wave superconductors in a magnetic field. The phase diagram of the
superconducting state, including the periodic Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) state in high magnetic fields, is discussed for different strengths of
quasiparticle many-body interactions within Landau's theory of Fermi liquids.
Decreasing the Fermi-liquid parameter causes the magnetic spin
susceptibility to increase, which in turn leads to a reduction of the FFLO
phase. It is shown that a negative results in a first-order phase
transition from the normal to the uniform superconducting state in a finite
temperature interval. Finally, we discuss the thermodynamic implications of a
first-order phase transition for CeCoIn.Comment: published version; removed direct comparison with experiment for the
upper critical field, as required by the referee
Magnetoconductivity of low-dimensional disordered conductors at the onset of the superconducting transition
Magnetoconductivity of the disordered two- and three-dimensional
superconductors is addressed at the onset of superconducting transition. In
this regime transport is dominated by the fluctuation effects and we account
for the interaction corrections coming from the Cooper channel. In contrast to
many previous studies we consider strong magnetic fields and various
temperature regimes, which allow to resolve the existing discrepancies with the
experiments. Specifically, we find saturation of the fluctuations induced
magneto-conductivity for both two- and three-dimensional superconductors at
already moderate magnetic fields and discuss possible dimensional crossover at
the immediate vicinity of the critical temperature. The surprising observation
is that closer to the transition temperature weaker magnetic field provides the
saturation. It is remarkable also that interaction correction to
magnetoconductivity coming from the Cooper channel, and specifically the so
called Maki-Thompson contribution, remains to be important even away from the
critical region.Comment: 4 pages, 1 figur
Binary fluid amplifier solves stability and load problems
Digital fluid amplifier has load intensity, high stability, and operates at low reynolds numbers. It contains specially designed nozzles to provide uniform exit-velocity profiles and to ensure jets of low turbulence
Suppression or enhancement of the Fulde-Ferrell-Larkin-Ovchinnikov order in a one-dimensional optical lattice with particle correlated tunnelling
We study through controlled numerical simulation the ground state properties
of spin-polarized strongly interacting fermi gas in an anisotropic optical
lattice, which is described by an effective one-dimensional general Hubbard
model with particle correlated hopping rate. We show that the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type of state, while enhanced by a
negative correlated hopping rate, can be completely suppressed by positive
particle correlated hopping, yielding to an unusual magnetic phase even for
particles with on-site attractive interaction We also find several different
phase separation patterns for these atoms in an inhomogeneous harmonic trap,
depending on the correlated hopping rate
Finite-Size Scaling Critical Behavior of Randomly Pinned Spin-Density Waves
We have performed Monte Carlo studies of the 3D model with random
uniaxial anisotropy, which is a model for randomly pinned spin-density waves.
We study simple cubic lattices, using values in the
range 16 to 64, and with random anisotropy strengths of = 1, 2, 3, 6
and . There is a well-defined finite temperature critical point, ,
for each these values of . We present results for the angle-averaged
magnetic structure factor, at for . We also use
finite-size scaling analysis to study scaling functions for the critical
behavior of the specific heat, the magnetization and the longitudinal magnetic
susceptibility. Good data collapse of the scaling functions over a wide range
of is seen for = 6 and . For our finite values of the scaled magnetization function increases with below , and
appears to approach an -independent limit for large . This suggests that
the system is ferromagnetic below .Comment: 21 pages in single column format, 20 .eps files, revised and
expanded, errors corrected, submitted to PR
The construction of a unit and workbook of exercises for the slow learner to develop comprehension and increase study skills for use in the teaching of an American history unit on the westward movement in the United States on a sixth grade level.
Thesis (Ed.M.)--Boston University
N.B.:pages missing: 170, 171, 173 from original cop
Towards the parameterisation of the Hubbard model for salts of BEDT-TTF: A density functional study of isolated molecules
We calculate the effective Coulomb repulsion between electrons/holes, U, and
site energy for an isolated BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene]
molecule in vacuo. U=4.2 \pm 0.1 eV for 44 experimental geometries taken from a
broad range of conformations, polymorphs, anions, temperatures, and pressures
(the quoted `error' is one standard deviation). Hence we conclude that U is
essentially the same for all of the compounds studied. This shows that the
strong (hydrostatic and chemical) pressure dependence observed in the phase
diagrams of the BEDT-TTF salts is not due to U. Therefore, if the Hubbard model
is sufficient to describe the phase diagram of the BEDT-TTF salts there must be
significant pressure dependence on the intramolecular terms in the Hamiltonian
and/or the reduction of the Hubbard U due to the interaction of the molecule
with the polarisable crystal environment. The renormalised value of U is
significantly smaller than the bare value of the Coulomb integral:
F_0=5.2\pm0.1 eV across the same set of geometries, emphasising the importance
of using the renormalised value of U. The site energy (for holes), xi=5.0\pm0.2
eV, varies only a little more than U across the same set of geometries.
However, we argue that this plays a key role in understanding the role of
disorder in ET salts in general and in explaining the difference between the
beta_L and beta_H phases of beta-(BEDT-TTF)_2I_3 in particular.Comment: 13 pages, 6 figures, also see animations at
http://www.youtube.com/watch?v=3K2kP8hWpZI,
http://www.youtube.com/watch?v=wIz1cRsSdEs and
http://www.youtube.com/watch?v=bNzUBAS6AFM, Expanded discussion of
renormalisation effects. To appear in J. Chem. Phy
Interplay between magnetism and superconductivity in Fe-pnictides
We consider phase transitions and potential co-existence of spin-density-wave
(SDW) magnetic order and extended s-wave () superconducting order within a
two-band itinerant model of iron pnictides, in which SDW magnetism and
superconductivity are competing orders. We show that depending on parameters,
the transition between these two states is either first order, or involves an
intermediate phase in which the two orders co-exist. We demonstrate that such
co-existence is possible when SDW order is incommensurate.Comment: 5 pages, 3 figure
Superfluid phases of triplet pairing and neutrino emission from neutron stars
Neutrino energy losses through neutral weak currents in the triplet-spin
superfluid neutron liquid are studied for the case of condensate involving
several magnetic quantum numbers. Low-energy excitations of the multicomponent
condensate in the timelike domain of the energy and momentum are analyzed.
Along with the well-known excitations in the form of broken Cooper pairs, the
theoretical analysis predicts the existence of collective waves of spin density
at very low energy. Because of a rather small excitation energy of spin waves,
their decay leads to a substantial neutrino emission at the lowest
temperatures, when all other mechanisms of neutrino energy loss are killed by a
superfluidity. Neutrino energy losses caused by the pair recombination and
spin-wave decays are examined in all of the multicomponent phases that might
represent the ground state of the condensate, according to modern theories, and
for the case when a phase transition occurs in the condensate at some
temperature. Our estimate predicts a sharp increase in the neutrino energy
losses followed by a decrease, along with a decrease in the temperature, that
takes place more rapidly than it would without the phase transition. We
demonstrate the important role of the neutrino radiation caused by the decay of
spin waves in the cooling of neutron stars.Comment: 24 pages, 5 figure
Nonequilibrium mesoscopic conductance fluctuations
We investigate the amplitude of mesoscopic fluctuations of the differential
conductance of a metallic wire at arbitrary bias voltage V. For non-interacting
electrons, the variance increases with V. The asymptotic large-V
behavior is \sim V/V_c (where eV_c=D/L^2 is the Thouless energy),
in agreement with the earlier prediction by Larkin and Khmelnitskii. We find,
however, that this asymptotics has a very small numerical prefactor and sets in
at very large V/V_c only, which strongly complicates its experimental
observation. This high-voltage behavior is preceded by a crossover regime,
V/V_c \lesssim 30, where the conductance variance increases by a factor \sim 3
as compared to its value in the regime of universal conductance fluctuations
(i.e., at V->0). We further analyze the effect of dephasing due to the
electron-electron scattering on at high voltages. With the Coulomb
interaction taken into account, the amplitude of conductance fluctuations
becomes a non-monotonic function of V. Specifically, drops as 1/V
for voltages V >> gV_c, where g is the dimensionless conductance. In this
regime, the conductance fluctuations are dominated by quantum-coherent regions
of the wire adjacent to the reservoirs.Comment: 14 pages, 4 figures. Fig.2 and one more appendix added, accepted for
publication in PR
- …