655 research outputs found
Topological Defects and the Spin Glass Phase of Cuprates
We propose that the spin glass phase of cuprates is due to the proliferation
of topological defects of a spiral distortion of the antiferromagnet order. Our
theory explains straightforwardly the simultaneous existence of short range
incommensurate magnetic correlations and complete a-b symmetry breaking in this
phase. We show via a renormalization group calculation that the collinear
O(3)/O(2) symmetry is unstable towards the formation of local non-collinear
correlations. A critical disorder strength is identified beyond which
topological defects proliferate already at zero temperature.Comment: 7 pages, 2 figures. Final version with some changes and one replaced
figur
Energy spectra of the ocean's internal wave field: theory and observations
The high-frequency limit of the Garrett and Munk spectrum of internal waves
in the ocean and the observed deviations from it are shown to form a pattern
consistent with the predictions of wave turbulence theory. In particular, the
high frequency limit of the Garrett and Munk spectrum constitutes an {\it
exact} steady state solution of the corresponding kinetic equation.Comment: 4 pages, one color figur
Differential approximation for Kelvin-wave turbulence
I present a nonlinear differential equation model (DAM) for the spectrum of
Kelvin waves on a thin vortex filament. This model preserves the original
scaling of the six-wave kinetic equation, its direct and inverse cascade
solutions, as well as the thermodynamic equilibrium spectra. Further, I extend
DAM to include the effect of sound radiation by Kelvin waves. I show that,
because of the phonon radiation, the turbulence spectrum ends at a maximum
frequency where
is the total energy injection rate, is the speed of sound and
is the quantum of circulation.Comment: Prepared of publication in JETP Letter
Theory of synthetic aperture radar ocean imaging: A MARSEN view
This paper reviews basic synthetic aperture radar (SAR) theory of ocean wave imaging mechanisms, using both known work and recent experimental and theoretical results from the Marine Remote Sensing (MARSEN) Experiment. Several viewpoints that have contributed to the field are drawn together in a general analysis of the backscatter statistics of a moving sea surface. A common focus for different scattering models is provided by the mean image impulse response function, which is shown to be identical to the (spatially varying) frequency variance spectrum of the local complex reflectivity coefficient. From the analysis has emerged a more complete view of the SAR imaging phenomenon than has been previously available. A new, generalized imaging model is proposed
Signature of stripe pinning in optical conductivity
The response of charge stripes to an external electric field applied
perpendicular to the stripe direction is studied within a diagrammatic approach
for both weak and strong pinning by random impurities. The sound-like mode of
the stripes described as elastic strings moves to finite frequency due to
impurity pinning. By calculating the optical conductivity we determine this
characteristic energy scale for both a single stripe and an array of
interacting stripes. The results explain the anomalous far-infrared peak
observed recently in optical-conductivity measurements on cuprates.Comment: Revised version, to appear in Phys. Rev.
Dynamics of lattice pinned charge stripes
We study the transversal dynamics of a charged stripe (quantum string) and
show that zero temperature quantum fluctuations are able to depin it from the
lattice. If the hopping amplitude t is much smaller than the string tension J,
the string is pinned by the underlying lattice. At t>>J, the string is depinned
and allowed to move freely, if we neglect the effect of impurities. By mapping
the system onto a 1D array of Josephson junctions, we show that the quantum
depinning occurs at t/J = 2 / pi^2. Besides, we exploit the relation of the
stripe Hamiltonian to the sine-Gordon theory and calculate the infrared
excitation spectrum of the quantum string for arbitrary t/J values.Comment: 4 pages, 2 figure
Structural effect on the static spin and charge correlations in LaBaSrCuO
We report the results of elastic neutron scattering measurements performed on
1/8-hole doped LaBaSrCuO single crystals with
{\it x}=0.05, 0.06, 0.075 and 0.085. In the low-temperature less-orthorhombic
(LTLO, {\it Pccn} symmetry) phase, the charge-density-wave (CDW) and
spin-density-wave (SDW) wavevectors were found to tilt in a low-symmetric
direction with one-dimensional anisotropy in the CuO plane, while they
were aligned along the high-symmetry axis in the low-temperature tetragonal
(LTT, {\it P}4/{\it ncm} symmetry) phase. The coincident direction of two
wavevectors suggests a close relation between CDW and SDW orders. The SDW
wavevector systematically deviates from the Cu-O bond direction in the LTLO
phase upon Sr substitution and the tilt angle in the LTLO phase is smaller than
that in the low-temperature orthorhombic phase (LTO, {\it B}{\it mab} symmetry)
with comparable in-plane orthorhombic distortion. These results demonstrate a
correlation between the corrugated pattern of CuO plane and the
deviations.Comment: 6 pages, 7figure
Antiferromagnetic Ising spin glass competing with BCS pairing interaction in a transverse field
The competition among spin glass (SG), antiferromagnetism (AF) and local
pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising
spin glass model with a local BCS pairing interaction in the presence of an
applied magnetic transverse field . In the present approach, spins in
different sublattices interact with a Gaussian random coupling with an
antiferromagnetic mean and standard deviation . The problem is
formulated in the path integral formalism in which spin operators are
represented by bilinear combinations of Grassmann variables. The saddle-point
Grand Canonical potential is obtained within the static approximation and the
replica symmetric ansatz. The results are analysed in phase diagrams in which
the AF and the SG phases can occur for small ( is the strength of the
local superconductor coupling written in units of ), while the PAIR phase
appears as unique solution for large . However, there is a complex line
transition separating the PAIR phase from the others. It is second order at
high temperature that ends in a tricritical point. The quantum fluctuations
affect deeply the transition lines and the tricritical point due to the
presence of .Comment: 16 pages, 6 figures, accepted Eur. Phys. J.
The gas of elastic quantum strings in 2+1 dimensions: finite temperatures
The finite temperature physics of the gas of elastic quantum strings as
introduced in J. Zaanen, Phys. Rev. Lett. 84, 753 is investigated. This model
is inspired on the stripes in the high Tc superconductors. We analyze in detail
how the kinetic interactions of the zero temperature quantum problem crossover
into the entropic interactions of the high temperature limit.Comment: 14 pages, 2 figure
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