339 research outputs found
Instanton correlators and phase transitions in two- and three-dimensional logarithmic plasmas
The existence of a discontinuity in the inverse dielectric constant of the
two-dimensional Coulomb gas is demonstrated on purely numerical grounds. This
is done by expanding the free energy in an applied twist and performing a
finite-size scaling analysis of the coefficients of higher-order terms. The
phase transition, driven by unbinding of dipoles, corresponds to the
Kosterlitz-Thouless transition in the 2D XY model. The method developed is also
used for investigating the possibility of a Kosterlitz-Thouless phase
transition in a three-dimensional system of point charges interacting with a
logarithmic pair-potential, a system related to effective theories of
low-dimensional strongly correlated systems. We also contrast the finite-size
scaling of the fluctuations of the dipole moments of the two-dimensional
Coulomb gas and the three-dimensional logarithmic system to those of the
three-dimensional Coulomb gas.Comment: 15 pages, 16 figure
Structural studies of liquid Co–Sn alloys
AbstractAn analysis of the structure features of liquid Co–Sn alloys has been performed by means of X-ray diffraction method, viscosity coefficient analysis and computer simulation method. The X-ray diffraction investigations were carried out over a wide concentration range at the temperature 1473K. It was found that the structure of these alloys can be described in the frame of independent X-ray scattering model. The viscosity coefficient was calculated by an excess entropy scaling and compared with experimental data
Deconfined fractional electric charges in graphene at high magnetic fields
The resistance at the charge neutral (Dirac) point was shown by Checkelsky et
al in Phys. Rev. B 79, 115434 (2009) to diverge upon the application of a
strong magnetic field normal to graphene. We argue that this divergence is the
signature for a Kekule instability of graphene, which is induced by the
magnetic field. We show that the strong magnetic field does not remove the zero
modes that bind a fraction of the electron around vortices in the Kekule
dimerization pattern, and that quenched disorder present in the system makes it
energetically possible to separate the fractional charges. These findings,
altogether, indicate that graphene can sustain deconfined fractionalized
electrons.Comment: 11 pages, 2 figure
gl(N|N) Super-Current Algebras for Disordered Dirac Fermions in Two Dimensions
We consider the non-hermitian 2D Dirac Hamiltonian with (A): real random
mass, imaginary scalar potential and imaginary gauge field potentials, and (B)
arbitrary complex random potentials of all three kinds. In both cases this
Hamiltonian gives rise to a delocalization transition at zero energy with
particle-hole symmetry in every realization of disorder. Case (A) is in
addition time-reversal invariant, and can also be interpreted as the
random-field XY Statistical Mechanics model in two dimensions. The
supersymmetric approach to disorder averaging results in current-current
perturbations of super-current algebras. Special properties of the
algebra allow the exact computation of the beta-functions, and of the
correlation functions of all currents. One of them is the Edwards-Anderson
order parameter. The theory is `nearly conformal' and possesses a
scale-invariant subsector which is not a current algebra. For N=1, in addition,
we obtain an exact solution of all correlation functions. We also study the
delocalization transition of case (B), with broken time reversal symmetry, in
the Gade-Wegner (Random-Flux) universality class, using a GL(N|N;C)/U(N|N)
sigma model, as well as its PSL(N|N) variant, and a corresponding generalized
random XY model. For N=1 the sigma model is shown to be identical to the
current-current perturbation. For the delocalization transitions (case (A) and
(B)) a density of states, diverging at zero energy, is found.Comment: LaTeX, 40 page
Excitation spectrum of the homogeneous spin liquid
We discuss the excitation spectrum of a disordered, isotropic and
translationally invariant spin state in the 2D Heisenberg antiferromagnet. The
starting point is the nearest-neighbor RVB state which plays the role of the
vacuum of the theory, in a similar sense as the Neel state is the vacuum for
antiferromagnetic spin wave theory. We discuss the elementary excitations of
this state and show that these are not Fermionic spin-1/2 `spinons' but spin-1
excited dimers which must be modeled by bond Bosons. We derive an effective
Hamiltonian describing the excited dimers which is formally analogous to spin
wave theory. Condensation of the bond-Bosons at zero temperature into the state
with momentum (pi,pi) is shown to be equivalent to antiferromagnetic ordering.
The latter is a key ingredient for a microscopic interpretation of Zhang's
SO(5) theory of cuprate superconductivityComment: RevTex-file, 16 PRB pages with 13 embedded eps figures. Hardcopies of
figures (or the entire manuscript) can be obtained by e-mail request to:
[email protected]
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