348 research outputs found
Anderson localization in Hubbard ladders
The effect of a weak random potential on two-leg Hubbard ladders is
investigated. The random potential is shown to induce Anderson localization
except for attractive enough interactions, supressing completely d-wave
superconductivity. These localization effects remain very strong even for many
ladders coupled by Josephson coupling. Both dc and ac conductivities and
localization lengths are obtained. Consequences for the superconducting ladder
compound SrCaCuO are discussed.Comment: 2 Pages, 2 Figures, Uses espcrc2.sty (included); Proceedings of the
SCES98 conference, July 1998 Paris, France; To be published in Physica
Disordered Quantum smectics
We study the impurity pinning of the Quantum Hall (QH) smectic state arising
in two dimensional electron systems in high Landau levels. We use replicas and
a Gaussian Variational method to deal with the disorder. The pinned quantum
smectic exhibits very anisotropic behaviour, with density correlations along
the direction of the stripes manifesting a Bragg-Glass type behaviour i.e.,
quasi long range order whereas those in the transverse direction are infra red
divergent. We calculate the dynamical conductivity along the stripe direction
and find a wavelength dependent pinning peak.Comment: 5 pages, one eps figure, revtex
Magnetostriction in an array of spin chains under magnetic field
We consider an array of XX spin-1/2 chains coupled to acoustic phonons and
placed in a magnetic field. Treating the phonons in the mean field
approximation, we show that this system presents a first order transition as a
function of the magnetic field between a partially magnetized distorted state
and the fully polarized undistorted state at low temperature. This behavior
results from the magnetostriction of the coupled chain system. A dip in the
elastic constant of the material near the saturation field along with an
anomaly in the magnetic susceptibility is predicted. We also predict the
contraction of the material as the magnetic field is reduced (positive
magnetostriction) and the reciprocal effect i.e. a decrease of magnetization
under applied pressure. At higher temperature, the first order transition is
replaced by a crossover. However, the anomalies in the susceptibilities in the
system near the saturation field are still present. We discuss the relevance of
our analysis in relation to recent experiments on spin-1/2 chain and ladder
materials in strong magnetic fields.Comment: 23 pages, Revtex 4, more detailed discussion of the connection with
Bose-Einstein condensation. Discussion of long range ordering by interladder
exchange, comparison with mean field theory. Some extra references adde
Competition of disorder and interchain hopping in a two-chain Hubbard model
We study the interplay of Anderson localization and interaction in a two
chain Hubbard ladder allowing for arbitrary ratio of disorder strength to
interchain coupling. We obtain three different types of spin gapped localized
phases depending on the strength of disorder: a pinned Charge Density
Wave (CDW) for weak disorder, a pinned
CDW for intermediate disorder and two independently pinned single chain
CDW for strong disorder.
Confinement of electrons can be obtained as a result of strong disorder or
strong attraction. We give the full phase diagram as a function of disorder,
interaction strength and interchain hopping. We also study the influence of
interchain hopping on localization length and show that localization is
enhanced by a small interchain hopping but suppressed by a large interchain
hopping.Comment: 12 pages, uses svjour and svepj macros, 8 EPS figure
Response functions in multicomponent Luttinger liquids
We derive an analytic expression for the zero temperature Fourier transform
of the density-density correlation function of a multicomponent Luttinger
liquid with different velocities. By employing Schwinger identity and a
generalized Feynman identity exact integral expressions are derived, and
approximate analytical forms are given for frequencies close to each component
singularity. We find power-like singularities and compute the corresponding
exponents. Numerical results are shown for the case of three components.Comment: 16 pages, two EPS figure
Kondo screening by the surface modes of a strong topological insulator
We consider a magnetic impurity deposited on the surface of a strong
topological insulator and interacting with the surface modes by a Kondo
exchange interaction. Taking into account the warping of the Fermi line of the
surface modes, we derive a mapping to an effective one dimensional model and
show that the impurity is fully screened by the surface electrons except when
the Fermi level lies exactly at the Dirac point. Using an Abrikosov fermion
mean-field theory, we calculate the shape of the electronic density Friedel
oscillation resulting from the presence of the Kondo screening cloud. We
analyze quantitatively the observability of a six-fold symmetry in the Friedel
oscillations for two prototype compounds: BiSe and BiTe.Comment: 22 pages, 6 figure
Raman Scattering cross section of Spin Ladders
The Raman scattering spectra from magnetic excitations in an
antiferromagnetic spin-1/2 two leg ladder is investigated for weak and strong
interladder coupling. In the first case, a cusp in the Raman intensityis
obtained at a frequency twice the gap. In the second case, a peak at twice the
gap replaces the cusp. We discuss the relevance of our calculation to recent
experiments on CaV2O5 and Sr14Cu24O41.Comment: RevTeX, 4 pages, 2 EPS Figure
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