2,954 research outputs found
Pairing in High Temperature Superconductors and Berry Phase
The topological approach to the understanding of pairing mechanism in high
superconductors analyses the relevance of the Berry phase factor in this
context. This also gives the evidence for the pairing mechanism to be of
magnetic origin.Comment: 6 page
Pairing via Index theorem
This work is motivated by a specific point of view: at short distances and
high energies the undoped and underdoped cuprates resemble the -flux phase
of the t-J model. The purpose of this paper is to present a mechanism by which
pairing grows out of the doped -flux phase. According to this mechanism
pairing symmetry is determined by a parameter controlling the quantum tunneling
of gauge flux quanta. For zero tunneling the symmetry is ,
while for large tunneling it is . A zero-temperature critical
point separates these two limits
Mesoscale simulations of surfactant dissolution and mesophase formation
The evolution of the contact zone between pure surfactant and solvent has
been studied by mesoscale simulation. It is found that mesophase formation
becomes diffusion controlled and follows the equilibrium phase diagram
adiabatically almost as soon as individual mesophases can be identified,
corresponding to times in real systems of order 10 microseconds.Comment: 4 pages, 2 figures, ReVTeX
Topological Quantum Phase Transitions in Topological Superconductors
In this paper we show that BF topological superconductors (insulators) exibit
phase transitions between different topologically ordered phases characterized
by different ground state degeneracy on manifold with non-trivial topology.
These phase transitions are induced by the condensation (or lack of) of
topological defects. We concentrate on the (2+1)-dimensional case where the BF
model reduce to a mixed Chern-Simons term and we show that the superconducting
phase has a ground state degeneracy and not . When the symmetry is
, namely when both gauge fields are compact, this model is
not equivalent to the sum of two Chern-Simons term with opposite chirality,
even if naively diagonalizable. This is due to the fact that U(1) symmetry
requires an ultraviolet regularization that make the diagonalization
impossible. This can be clearly seen using a lattice regularization, where the
gauge fields become angular variables. Moreover we will show that the phase in
which both gauge fields are compact is not allowed dynamically.Comment: 5 pages, no figure
Coarse-grained simulation of amphiphilic self-assembly
We present a computer simulation study of amphiphilic self assembly performed using a computationally efficient single-site model based on Gay-Berne and Lennard-Jones particles. Molecular dynamics simulations of these systems show that free self-assembly of micellar, bilayer and inverse micelle arrangements can be readily achieved for a single model parameterisation. This self-assembly is predominantly driven by the anisotropy of the amphiphile-solvent interaction, amphiphile-amphiphile interactions being found to be of secondary importance. While amphiphile concentration is the main determinant of phase stability, molecular parameters such as headgroup size and interaction strength also have measurable affects on system properties. </p
Structural properties of electrons in quantum dots in high magnetic fields: Crystalline character of cusp states and excitation spectra
The crystalline or liquid character of the downward cusp states in N-electron
parabolic quantum dots (QD's) at high magnetic fields is investigated using
conditional probability distributions obtained from exact diagonalization.
These states are of crystalline character for fractional fillings covering both
low and high values, unlike the liquid Jastrow-Laughlin wave functions, but in
remarkable agreement with the rotating-Wigner-molecule ones [Phys. Rev. B 66,
115315 (2002)]. The crystalline arrangement consists of concentric polygonal
rings that rotate independently of each other, with the electrons on each ring
rotating coherently. We show that the rotation stabilizes the Wigner molecule
relative to the static one defined by the broken-symmetry
unrestricted-Hartree-Fock solution. We discuss the non-rigid behavior of the
rotating Wigner molecule and pertinent features of the excitation spectrum,
including the occurrence of a gap between the ground and first excited states
that underlies the incompressibility of the system. This leads us to conjecture
that the rotating crystal (and not the static one) remains the relevant ground
state for low fractional fillings even at the thermodynamic limit.Comment: Published version. Typos corrected. REVTEX4. 10 pages with 8
postscript figures (5 in color). For related papers, see
http://www.prism.gatech.edu/~ph274cy
An extended Hubbard model with ring exchange: a route to a non-Abelian topological phase
We propose an extended Hubbard model on a 2D Kagome lattice with an
additional ring-exchange term. The particles can be either bosons or spinless
fermions . At a special filling fraction of 1/6 the model is analyzed in the
lowest non-vanishing order of perturbation theory. Such ``undoped'' model is
closely related to the Quantum Dimer Model. We show how to arrive at an exactly
soluble point whose ground state manifold is the extensively degenerate
``d-isotopy space'', a necessary precondition for for a certain type of
non-Abelian topological order. Near the ``special'' values, , this space is expected to collapse to a stable topological phase
with anyonic excitations closely related to SU(2) Chern-Simons theory at level
k.Comment: 4 pages, 2 colour figures, submitted to PRL. For an extended
treatment of a more general family of models see cond-mat/030912
Atomic swelling upon compression
The hydrogen atom under the pressure of a spherical penetrable confinement
potential of a decreasing radius is explored, as a case study. A novel
counter-intuitive effect of atomic swelling rather than shrinking with
decreasing is unraveled, when reaches, and remains smaller
than, a certain critical value. Upon swelling, the size of the atom is shown to
increase by an order of magnitude, or more, compared to the size of the free
atom. Examples of changes of photoabsorption properties of confined hydrogen
atom upon its swelling are uncovered and demonstrated.Comment: 5 pages, 4 figure
Cumulative and Differential Effects of Early Child Care and Middle Childhood Out-of-School Time on Adolescent Functioning.
Effects associated with early child care and out-of-school time (OST) during middle childhood were examined in a large sample of U.S. adolescents (N = 958). Both higher quality early child care AND more epochs of organized activities (afterschool programs and extracurricular activities) during middle childhood were linked to higher academic achievement at age 15. Differential associations were found in the behavioral domain. Higher quality early child care was associated with fewer externalizing problems, whereas more hours of early child care was linked to greater impulsivity. More epochs of organized activities was associated with greater social confidence. Relations between early child care and adolescent outcomes were not mediated or moderated by OST arrangements in middle childhood, consistent with independent, additive relations of these nonfamilial settings
Thermal properties of gauge-fields common to anyon superconductors and spin-liquids
The thermally driven confinement-deconfinement transition exhibited by
lattice quantum electrodynamics in two space dimensions is re-examined in the
context of the statistical gauge-fields common to anyon superconductors and to
spin-liquids. Particle-hole excitations in both systems are bound by a
confining string at temperatures below the transition temperature . We
argue that coincides with the actual critical temperature for anyon
superconductivity. The corresponding specific-heat contribution, however, shows
a {\it smooth} peak just below characteristic of certain high-temperature
superconductors.Comment: 13 pgs, TeX, to appear in Physical Review B (minor revisions
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