3,554 research outputs found
Baryonic Bound State of Vortices in Multicomponent Superconductors
We construct a bound state of three 1/3-quantized Josephson coupled vortices
in three-component superconductors with intrinsic Josephson couplings, which
may be relevant with regard to iron-based superconductors. We find a Y-shaped
junction of three domain walls connecting the three vortices, resembling the
baryonic bound state of three quarks in QCD. The appearance of the Y-junction
(but not a Delta-junction) implies that in both cases of superconductors and
QCD, the bound state is described by a genuine three-body interaction (but not
by the sum of two-body interactions). We also discuss a
confinement/deconfinement phase transition.Comment: 11 pages, 3 figures, one section on confinement/deconfinement
transition added, published versio
Phase Fluctuations and Pseudogap Properties: Influence of Nonmagnetic Impurities
The presence of nonmagnetic impurities in a 2D ``bad metal'' depresses the
superconducting Berezinskii-Kosterlitz-Thouless transition temperature, while
leaving the pairing energy scale unchanged. Thus the region of the pseudogap
non-superconducting phase, where the modulus of the order parameter is non-zero
but its phase is random, and which opens at the pairing temperature is
substantially bigger than for the clean system. This supports the premise that
fluctuations in the phase of the order parameter can in principle describe the
pseudogap phenomena in high- materials over a rather wide range of
temperatures and carrier densities. The temperature dependence of the bare
superfluid density is also discussed.Comment: 11 pages, LaTeX, 1 EPS figure; final version to appear in
Low.Temp.Phy
BCS-Bose Crossover in Color Superconductivity
It is shown that the onset of the color superconducting phase occurs in the
BCS-BE crossover region.Comment: 5 pages, LaTeX, references adde
Mesonic Wavefunctions in the three-dimensional Gross-Neveu model
We present results from a numerical study of bound state wavefunctions in the
(2+1)-dimensional Gross-Neveu model with staggered lattice fermions at both
zero and nonzero temperature. Mesonic channels with varying quantum numbers are
identified and analysed. In the strongly coupled chirally broken phase at T=0
the wavefunctions expose effects due to varying the interaction strength more
effectively than straightforward spectroscopy. In the weakly coupled chirally
restored phase information on fermion - antifermion scattering is recovered. In
the hot chirally restored phase we find evidence for a screened interaction.
The T=0 chirally symmetric phase is most readily distinguished from the
symmetric phase at high T via the fermion dispersion relation.Comment: 18 page
Temperature-doping phase diagram of layered superconductors
The superconducting properties of a layered system are analyzed for the cases
of zero- and non-zero angular momentum of the pairs. The effective
thermodynamic potential for the quasi-2D XY-model for the gradients of the
phase of the order parameter is derived from the microscopic superconducting
Hamiltonian. The dependence of the superconducting critical temperature T_c on
doping, or carrier density, is studied at different values of coupling and
inter-layer hopping. It is shown that the critical temperature T_c of the
layered system can be lower than the critical temperature of the
two-dimensional Berezinskii-Kosterlitz-Thouless transition T_BKT at some values
of the model parameters, contrary to the case when the parameters of the
XY-model do not depend on the microscopic Hamiltonian parameters.Comment: To be published in Phys. Rev.
Possible Pseudogap Phase in QCD
Thermal pion fluctuations, in principle, can completely disorder the phase of
the quark condensate and thus restore chiral symmetry. If this happens before
the quark condensate melts, strongly-interacting matter will be in the
pseudogap state just above the chiral phase transition. The quark condensate
does not vanish locally and quarks acquire constituent masses in the pseudogap
phase, despite chiral symmetry is restored.Comment: 8 pages, 1 figure; v2: references added; v3: argumerts modified; v4:
minor changes; v5: a misprint correcte
The Coupled Electron-Ion Monte Carlo Method
In these Lecture Notes we review the principles of the Coupled Electron-Ion
Monte Carlo methods and discuss some recent results on metallic hydrogen.Comment: 38 pages, 6 figures, Lecture notes for the International School of
Solid State Physics, 34th course: "Computer Simulation in Condensed Matter:
from Materials to Chemical Biology", 20 July-1 August 2005 Erice (Italy). To
appear in Lecture Notes in Physics (2006
Comparison of some Reduced Representation Approximations
In the field of numerical approximation, specialists considering highly
complex problems have recently proposed various ways to simplify their
underlying problems. In this field, depending on the problem they were tackling
and the community that are at work, different approaches have been developed
with some success and have even gained some maturity, the applications can now
be applied to information analysis or for numerical simulation of PDE's. At
this point, a crossed analysis and effort for understanding the similarities
and the differences between these approaches that found their starting points
in different backgrounds is of interest. It is the purpose of this paper to
contribute to this effort by comparing some constructive reduced
representations of complex functions. We present here in full details the
Adaptive Cross Approximation (ACA) and the Empirical Interpolation Method (EIM)
together with other approaches that enter in the same category
Application of the Maximum Entropy Method to the (2+1)d Four-Fermion Model
We investigate spectral functions extracted using the Maximum Entropy Method
from correlators measured in lattice simulations of the (2+1)-dimensional
four-fermion model. This model is particularly interesting because it has both
a chirally broken phase with a rich spectrum of mesonic bound states and a
symmetric phase where there are only resonances. In the broken phase we study
the elementary fermion, pion, sigma and massive pseudoscalar meson; our results
confirm the Goldstone nature of the pi and permit an estimate of the meson
binding energy. We have, however, seen no signal of sigma -> pi pi decay as the
chiral limit is approached. In the symmetric phase we observe a resonance of
non-zero width in qualitative agreement with analytic expectations; in addition
the ultra-violet behaviour of the spectral functions is consistent with the
large non-perturbative anomalous dimension for fermion composite operators
expected in this model.Comment: 25 pages, 13 figure
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