2,905 research outputs found
Spin-spin Correlation lengths of Bilayer Antiferromagnets
The spin-spin correlation length and the static structure factor for bilayer
antiferromagnets, such as YBaCuO, are calculated using field
theoretical and numerical methods. It is shown that these quantities can be
directly measured in neutron scattering experiments using energy integrated
two-axis scan despite the strong intensity modulation perpendicular to the
layers. Our calculations show that the correlation length of the bilayer
antiferromagnet diverges considerably more rapidly, as the temperature tends to
zero, than the correlation length of the corresponding single layer
antiferromagnet typified by LaCuO. This rapid divergence may have
important consequences with respect to magnetic fluctuations of the doped
superconductors.Comment: This paper supersedes cond-mat/9703138 and contains numerical
simulation results to compare against analytical results. 6 pages, 2
postscript figures (embedded), uses EuroPhys.sty and EuroMac
The effects of magnetic field on the d-density wave order in the cuprates
We consider the effects of a perpendicular magnetic field on the d-density
wave order and conclude that if the pseudogap phase in the cuprates is due to
this order, then it is highly insensitive to the magnetic field in the
underdoped regime, while its sensitivity increases as the gap vanishes in the
overdoped regime. This appears to be consistent with the available experiments
and can be tested further in neutron scattering experiments. We also
investigate the nature of the de Haas- van Alphen effect in the ordered state
and discuss the possibility of observing it.Comment: 5 pages, 4 eps figures, RevTex4. Corrected a silly but important typo
in the abstrac
An Experimental Study of Parabolic Wire-reflectors on a Wave-length of About 3 Metres
Abstract not Availabl
Correlation Lengths in Quantum Spin Ladders
Analytic expressions for the correlation length temperature dependences are
given for antiferromagnetic spin-1/2 Heisenberg ladders using a finite-size
non-linear sigma-model approach. These calculations rely on identifying three
successive crossover regimes as a function of temperature. In each of these
regimes, precise and controlled approximations are formulated. The analytical
results are found to be in excellent agreement with Monte Carlo simulations for
the Heisenberg Hamiltonian.Comment: 5 pages LaTeX using RevTeX, 3 encapsulated postscript figure
Bound states in d-density-wave phases
We investigate the quasiparticle spectrum near surfaces in a two-dimensional
system with d-density-wave order within a mean-field theory. For Fermi surfaces
with perfect nesting for the ordering wave vector of the d-density-wave, a zero
energy bound state occurs at [110] surfaces, in close analogy with the known
effect in d-wave superconducting states or graphite. When the shape of the
Fermi surface is changed by doping, the bound state energy moves away from the
Fermi level. Furthermore, away from half-filling we find inhomogeneous phases
with domain walls of the d-density-wave order parameter. The domain walls also
support low energy bound states. These phenomena might provide an experimental
test for hidden d-density-wave order in the high-Tc cuprates.Comment: 6 pages, 5 figure
Semiclassical Theory of Chaotic Quantum Transport
We present a refined semiclassical approach to the Landauer conductance and
Kubo conductivity of clean chaotic mesoscopic systems. We demonstrate for
systems with uniformly hyperbolic dynamics that including off-diagonal
contributions to double sums over classical paths gives a weak-localization
correction in quantitative agreement with results from random matrix theory. We
further discuss the magnetic field dependence. This semiclassical treatment
accounts for current conservation.Comment: 4 pages, 1 figur
Single hole doped strongly correlated ladder with a static impurity
We consider a strongly correlated ladder with diagonal hopping and exchange
interactions described by type hamiltonian. We study the dynamics of a
single hole in this model in the presence of a static non-magnetic (or
magnetic) impurity. In the case of a non-magnetic (NM) impurity we solve the
problem analytically both in the triplet (S=1) and singlet (S=0) sectors. In
the triplet sector the hole doesn't form any bound state with the impurity.
However, in the singlet sector the hole forms bound states of different
symmetries with increasing values. Binding energies of those
impurity-hole bound states are compared with the binding energy of a pair of
holes in absence of any impurity. In the case of magnetic impurity the
analytical eigenvalue equations are solved for a large (50 X 2) lattice. In
this case also, with increasing values, impurity-hole bound states of
different symmetries are obtained. Binding of the hole with the impurity is
favoured for the case of a ferromagnetic (FM) impurity than in the case of
antiferromagnetic (AFM) impurity. However binding energy is found to be maximum
for the NM impurity. Comparison of binding energies and various impurity-hole
correlation functions indicates a pair breaking mechanism by NM impurity.Comment: 15 Pages, 6 figure
Theory of d-density wave viewed from a vertex model and its implications
The thermal disordering of the -density wave, proposed to be the origin of
the pseudogap state of high temperature superconductors, is suggested to be the
same as that of the statistical mechanical model known as the 6-vertex model.
The low temperature phase consists of a staggered order parameter of
circulating currents, while the disordered high temperature phase is a
power-law phase with no order. A special feature of this transition is the
complete lack of an observable specific heat anomaly at the transition. There
is also a transition at a even higher temperature at which the magnitude of the
order parameter collapses. These results are due to classical thermal
fluctuations and are entirely unrelated to a quantum critical point in the
ground state. The quantum mechanical ground state can be explored by
incorporating processes that causes transitions between the vertices, allowing
us to discuss quantum phase transition in the ground state as well as the
effect of quantum criticality at a finite temperature as distinct from the
power-law fluctuations in the classical regime. A generalization of the model
on a triangular lattice that leads to a 20-vertex model may shed light on the
Wigner glass picture of the metal-insulator transition in two-dimensional
electron gas. The power-law ordered high temperature phase may be generic to a
class of constrained systems and its relation to recent advances in the quantum
dimer models is noted.Comment: RevTex4, 10 pages, 11 figure
Dynamical simulation of current fluctuations in a dissipative two-state system
Current fluctuations in a dissipative two-state system have been studied
using a novel quantum dynamics simulation method. After a transformation of the
path integrals, the tunneling dynamics is computed by deterministic integration
over the real-time paths under the influence of colored noise. The nature of
the transition from coherent to incoherent dynamics at low temperatures is
re-examined.Comment: 4 pages, 4 figures; to appear in Phys. Rev. Letter
Anomalous scaling and spin-charge separation in coupled chains
We use a bosonization approach to show that the three dimensional Coulomb
interaction in coupled metallic chains leads to a Luttinger liquid for
vanishing inter-chain hopping , and to a Fermi liquid for any finite
. However, for small the Greens-function satisfies
a homogeneity relation with a non-trivial exponent in a large
intermediate regime. Our results offer a simple explanation for the large
values of inferred from recent photoemission data from quasi
one-dimensional conductors and might have some relevance for the understanding
of the unusual properties of the high-temperature superconductors.Comment: compressed and uuencoded ps-file, including the figures, accepted for
publication in Phys. Rev. Lett
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