15,435 research outputs found
Band structure of Charge Ordered Doped Antiferromagnets
We study the distribution of electronic spectral weight in a doped
antiferromagnet with various types of charge order and compare to angle
resolved photoemission experiments on lightly doped LaSrCuO
(LSCO) and electron doped NdCeCuO. Calculations on
in-phase stripe and bubble phases for the electron doped system are both in
good agreement with experiment including in particular the existence of in-gap
spectral weight. In addition we find that for in-phase stripes, in contrast to
anti-phase stripes, the chemical potential is likely to move with doping. For
the hole doped system we find that ``staircase'' stripes which are globally
diagonal but locally vertical or horizontal can reproduce the photoemission
data whereas pure diagonal stripes cannot. We also calculate the magnetic
structure factors of such staircase stripes and find that as the stripe
separation is decreased with increased doping these evolve from diagonal to
vertical separated by a coexistence region. The results suggest that the
transition from horizontal to diagonal stripes seen in neutron scattering on
underdoped LSCO may be a crossover between a regime where the typical length of
straight stripe segments is longer than the inter-stripe spacing to one where
it is shorter and that locally the stripes are always aligned with the Cu-O
bonds.Comment: 13 pages, 16 figure
Infinitesimal Variations of Hodge Structure at Infinity
By analyzing the local and infinitesimal behavior of degenerating polarized
variations of Hodge structure the notion of infinitesimal variation of Hodge
structure at infinity is introduced. It is shown that all such structures can
be integrated to polarized variations of Hodge structure and that, conversely,
all are limits of infinitesimal variations of Hodge structure (IVHS) at finite
points. As an illustration of the rich information encoded in this new
structure, some instances of the maximal dimension problem for this type of
infinitesimal variation are presented and contrasted with the "classical" case
of IVHS at finite points
Nodal-antinodal dichotomy and magic doping fractions in a stripe ordered antiferromagnet
We study a model of a stripe ordered doped antiferromagnet consisting of
coupled Hubbard ladders which can be tuned from quasi-one-dimensional to
two-dimensional. We solve for the magnetization and charge density on the
ladders by Hartree-Fock theory and find a set of solutions with lightly doped
``spin-stripes'' which are antiferromagnetic and more heavily doped anti-phase
``charge-stripes''. Both the spin- and charge-stripes have electronic spectral
weight near the Fermi energy but in different regions of the Brillouin zone;
the spin-stripes in the ``nodal'' region, near (\pi/2,\pi/2), and the
charge-stripes in the ``antinodal'' region, near (\pi,0). We find a striking
dichotomy between nodal and antinodal states in which the nodal states are
essentially delocalized and two-dimensional whereas the antinodal states are
quasi-one-dimensional, localized on individual charge-stripes. For
bond-centered stripes we also find an even-odd effect of the charge periodicity
which could explain the non-monotonous variations with doping of the
low-temperature resistivity in LSCOComment: 6 pages, 6 figures, Expanded and improved, with additional reference
Electric arc device for heating gases Patent
Electric arc device for minimizing electrode ablation and heating gases to supersonic or hypersonic wind tunnel temperature
Monolayer charged quantum films: A quantum simulation study
We use path-integral Monte Carlo (PIMC) to study the effects of adding a
long-range repulsive Coulomb interaction to the usual Van der Waals interaction
between two atoms of a submonolayer quantum film such as helium on graphite or
a pure two-dimensional superfluid. Such interactions frustrate or compete with
the natural tendency of the system for phase separation namely to form a
macroscopic liquid or solid phase. We find that as a function of the relative
strength of the long-range repulsion, surface coverage and temperature, the
system undergoes a series of transformations, including a triangular
Wigner-like crystal of clusters, a charge stripe-ordered phase and a fluid
phase. The goal of these studies is to understand the role of quantum
fluctuations when such competing interactions appear together with formation of
preexisting electron pairs as might be the case in cuprate superconductors.Comment: 10 pages, 7 figures to be published in International Journal of
Modern Physics
"Exact" Algorithm for Random-Bond Ising Models in 2D
We present an efficient algorithm for calculating the properties of Ising
models in two dimensions, directly in the spin basis, without the need for
mapping to fermion or dimer models. The algorithm gives numerically exact
results for the partition function and correlation functions at a single
temperature on any planar network of N Ising spins in O(N^{3/2}) time or less.
The method can handle continuous or discrete bond disorder and is especially
efficient in the case of bond or site dilution, where it executes in O(L^2 ln
L) time near the percolation threshold. We demonstrate its feasibility on the
ferromagnetic Ising model and the +/- J random-bond Ising model (RBIM) and
discuss the regime of applicability in cases of full frustration such as the
Ising antiferromagnet on a triangular lattice.Comment: 4.2 pages, 5 figures, accepted for publication in Phys. Rev. Let
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