986 research outputs found

### High-temperature expansions through order 24 for the two-dimensional classical XY model on the square lattice

The high-temperature expansion of the spin-spin correlation function of the
two-dimensional classical XY (planar rotator) model on the square lattice is
extended by three terms, from order 21 through order 24, and analyzed to
improve the estimates of the critical parameters.Comment: 7 pages, 2 figure

### Kosterlitz-Thouless transition of the quasi two-dimensional trapped Bose gas

We present Quantum Monte Carlo calculations with up to N=576000 interacting
bosons in a quasi two-dimensional trap geometry closely related to recent
experiments with atomic gases. The density profile of the gas and the
non-classical moment of inertia yield intrinsic signatures for the
Kosterlitz--Thouless transition temperature T_KT. From the reduced one-body
density matrix, we compute the condensate fraction, which is quite large for
small systems. It decreases slowly with increasing system sizes, vanishing in
the thermodynamic limit. We interpret our data in the framework of the
local-density approximation, and point out the relevance of our results for the
analysis of experiments.Comment: 4 pages, 4 figure

### Generalized scaling theory for critical phenomena including essential singularity and infinite dimensionality

We propose a generic scaling theory for critical phenomena that includes
power-law and essential singularities in finite and infinite dimensional
systems. In addition, we clarify its validity by analyzing the Potts model in a
simple hierarchical network, where a saddle-node bifurcation of the
renormalization-group fixed point governs the essential singularity.Comment: 5 pages, 3 figure

### Critical exponents of the O(N) model in the infrared limit from functional renormalization

We determined the critical exponent $\nu$ of the scalar O(N) model with a
strategy based on the definition of the correlation length in the infrared
limit. The functional renormalization group treatment of the model shows that
there is an infrared fixed point in the broken phase. The appearing degeneracy
induces a dynamical length scale there, which can be considered as the
correlation length. It is shown that the IR scaling behavior can account either
for the Ising type phase transition in the 3-dimensional O(N) model, or for the
Kosterlitz-Thouless type scaling of the 2-dimensional O(2) model.Comment: final version, 7 pages 7 figures, to appear in Phys. Rev.

### Phase transition in site-diluted Josephson junction arrays: A numerical study

We numerically investigate the intriguing effects produced by random
percolative disorder in two-dimensional Josephson-junction arrays. By dynamic
scaling analysis, we evaluate critical temperatures and critical exponents with
high accuracy. It is observed that, with the introduction of site-diluted
disorder, the Kosterlitz-Thouless phase transition is eliminated and evolves
into a continuous transition with power-law divergent correlation length.
Moreover, genuine depinning transition and creep motion are studied, evidence
for distinct creep motion types is provided. Our results not only are in good
agreement with the recent experimental findings, but also shed some light on
the relevant phase transitions.Comment: 7 pages, 8 figures, Phys. Rev. B (in press

### Spontaneous current generation in the gapless 2SC phase

It is found that, except chromomagnetic instability, the gapless 2SC phase
also exhibits a paramagnetic response to the perturbation of an external color
neutral baryon current. The spontaneously generated baryon current driven by
the mismatch is equivalent to the one-plane wave LOFF state. We describe the
2SC phase in the nonlinear realization framework, and show that each
instability indicates the spontaneous generation of the corresponding pseudo
Nambu-Golstone current. We show this Nambu-Goldstone currents generation state
covers the gluon phase as well as the one-plane wave LOFF state. We further
point out that, when charge neutrality condition is required, there exists a
narrow unstable LOFF (Us-LOFF) window, where not only off-diagonal gluons but
the diagonal 8-th gluon cannot avoid the magnetic instability. We discuss that
the diagonal magnetic instability in this Us-LOFF window cannot be cured by
off-diagonal gluon condensate in color superconducting phase, and it will also
show up in some constrained Abelian asymmetric superfluid/superconducting
system.Comment: 8 pages, no figure, final version to appear in PR

### Odd Triplet Pairing in clean Superconductor/Ferromagnet heterostructures

We study triplet pairing correlations in clean Ferromagnet (F)/Superconductor
(S) nanojunctions, via fully self consistent solution of the Bogoliubov-de
Gennes equations. We consider FSF trilayers, with S being an s-wave
superconductor, and an arbitrary angle $\alpha$ between the magnetizations of
the two F layers. We find that contrary to some previous expectations, triplet
correlations, odd in time, are induced in both the S and F layers in the clean
limit. We investigate their behavior as a function of time, position, and
$\alpha$. The triplet amplitudes are largest at times on the order of the
inverse ``Debye'' frequency, and at that time scale they are long ranged in
both S and F. The zero temperature condensation energy is found to be lowest
when the magnetizations are antiparallel.Comment: Four pages, including four figure

### Application of the lattice Green's function for calculating the resistance of an infinite networks of resistors

We calculate the resistance between two arbitrary grid points of several
infinite lattice structures of resistors by using lattice Green's functions.
The resistance for $d$ dimensional hypercubic, rectangular, triangular and
honeycomb lattices of resistors is discussed in detail. We give recurrence
formulas for the resistance between arbitrary lattice points of the square
lattice. For large separation between nodes we calculate the asymptotic form of
the resistance for a square lattice and the finite limiting value of the
resistance for a simple cubic lattice. We point out the relation between the
resistance of the lattice and the van Hove singularity of the tight-binding
Hamiltonian. Our Green's function method can be applied in a straightforward
manner to other types of lattice structures and can be useful didactically for
introducing many concepts used in condensed matter physics

### Two-Dimensional Order and Disorder Thermofields

The main objective of this paper was to obtain the two-dimensional order and
disorder thermal operators using the Thermofield Bosonization formalism. We
show that the general property of the two-dimensional world according with the
bosonized Fermi field at zero temperature can be constructed as a product of an
order and a disorder variables which satisfy a dual field algebra holds at
finite temperature. The general correlation functions of the order and disorder
thermofields are obtained.Comment: 4 page

### Frequency-Temperature Crossover in the Conductivity of Disordered Luttinger Liquids

The temperature ($T$) and frequency ($\omega$) dependent conductivity of
weakly disordered Luttinger liquids is calculated in a systematic way both by
perturbation theory and from a finite temperature renormalization group (RG)
treatment to leading order in the disorder strength. Whereas perturbation
theory results in $\omega/T$ scaling of the conductivity such scaling is
violated in the RG traetment. We also determine the non-linear field dependence
of the conductivity, whose power law scaling is different from that of
temperature and frequency dependence.Comment: 4 pages, 4 figure

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