6,524 research outputs found
Electronic Phase Separation Transition as the Origin of the Superconductivity and the Pseudogap Phase of Cuprates
We propose a new phase of matter, an electronic phase separation transition
that starts near the upper pseudogap and segregates the holes into high and low
density domains. The Cahn-Hilliard approach is used to follow quantitatively
this second order transition. The resulting grain boundary potential confines
the charge in domains and favors the development of intragrain superconducting
amplitudes. The zero resistivity transition arises only when the intergrain
Josephson coupling is of the order of the thermal energy and phase
locking among the superconducting grains takes place. We show that this
approach explains the pseudogap and superconducting phases in a natural way and
reproduces some recent scanning tunneling microscopy dataComment: 4 pages and 5 eps fig
Statistical wave scattering through classically chaotic cavities in the presence of surface absorption
We propose a model to describe the statistical properties of wave scattering
through a classically chaotic cavity in the presence of surface absorption.
Experimentally, surface absorption could be realized by attaching an "absorbing
patch" to the inner wall of the cavity. In our model, the cavity is connected
to the outside by a waveguide with N open modes (or channels), while an
experimental patch is simulated by an "absorbing mirror" attached to the inside
wall of the cavity; the mirror, consisting of a waveguide that supports Na
channels, with absorption inside and a perfectly reflecting wall at its end, is
described by a subunitary scattering matrix Sa. The number of channels Na, as a
measure of the geometric cross section of the mirror, and the lack of unitarity
of Sa as a measure of absorption, are under our control: these parameters have
an important physical significance for real experiments. The absorption
strength in the cavity is quantified by the trace of the lack of unitarity. The
statistical distribution of the resulting S matrix for N=1 open channel and
only one absorbing channel, Na =1, is solved analytically for the orthogonal
and unitary universality classes, and the results are compared with those
arising from numerical simulations. The relation with other models existing in
the literature, in some of which absorption has a volumetric character, is also
studied.Comment: 6 pages, 3 figures, submitted to Phys. Rev.
Statistical fluctuations of the parametric derivative of the transmission and reflection coefficients in absorbing chaotic cavities
Motivated by recent theoretical and experimental works, we study the
statistical fluctuations of the parametric derivative of the transmission T and
reflection R coefficients in ballistic chaotic cavities in the presence of
absorption. Analytical results for the variance of the parametric derivative of
T and R, with and without time-reversal symmetry, are obtained for both
asymmetric and left-right symmetric cavities. These results are valid for
arbitrary number of channels, in completely agreement with the one channel case
in the absence of absorption studied in the literature.Comment: Modified version as accepted in PR
Task planning and control synthesis for robotic manipulation in space applications
Space-based robotic systems for diagnosis, repair and assembly of systems will require new techniques of planning and manipulation to accomplish these complex tasks. Results of work in assembly task representation, discrete task planning, and control synthesis which provide a design environment for flexible assembly systems in manufacturing applications, and which extend to planning of manipulatiuon operations in unstructured environments are summarized. Assembly planning is carried out using the AND/OR graph representation which encompasses all possible partial orders of operations and may be used to plan assembly sequences. Discrete task planning uses the configuration map which facilitates search over a space of discrete operations parameters in sequential operations in order to achieve required goals in the space of bounded configuration sets
Exact Solution for the Distribution of Transmission Eigenvalues in a Disordered Wire and Comparison with Random-Matrix Theory
An exact solution is presented of the Fokker-Planck equation which governs
the evolution of an ensemble of disordered metal wires of increasing length, in
a magnetic field. By a mapping onto a free-fermion problem, the complete
probability distribution function of the transmission eigenvalues is obtained.
The logarithmic eigenvalue repulsion of random-matrix theory is shown to break
down for transmission eigenvalues which are not close to unity. ***Submitted to
Physical Review B.****Comment: 20 pages, REVTeX-3.0, INLO-PUB-931028
Equivalence of Fokker-Planck approach and non-linear -model for disordered wires in the unitary symmetry class
The exact solution of the Dorokhov-Mello-Pereyra-Kumar-equation for quasi
one-dimensional disordered conductors in the unitary symmetry class is employed
to calculate all -point correlation functions by a generalization of the
method of orthogonal polynomials. We obtain closed expressions for the first
two conductance moments which are valid for the whole range of length scales
from the metallic regime () to the insulating regime () and
for arbitrary channel number. In the limit (with )
our expressions agree exactly with those of the non-linear -model
derived from microscopic Hamiltonians.Comment: 9 pages, Revtex, one postscript figur
Insensitivity to Time-Reversal Symmetry Breaking of Universal Conductance Fluctuations with Andreev Reflection
Numerical simulations of conduction through a disordered microbridge between
a normal metal and a superconductor have revealed an anomalous insensitivity of
the conductance fluctuations to a magnetic field. A theory for the anomaly is
presented: Both an exact analytical calculation (using random-matrix theory)
and a qualitative symmetry argument (involving the exchange of time-reversal
for reflection symmetry).Comment: 8 pages, REVTeX-3.0, 2 figure
Intensity correlations in electronic wave propagation in a disordered medium: the influence of spin-orbit scattering
We obtain explicit expressions for the correlation functions of transmission
and reflection coefficients of coherent electronic waves propagating through a
disordered quasi-one-dimensional medium with purely elastic diffusive
scattering in the presence of spin-orbit interactions. We find in the metallic
regime both large local intensity fluctuations and long-range correlations
which ultimately lead to universal conductance fluctuations. We show that the
main effect of spin-orbit scattering is to suppress both local and long-range
intensity fluctuations by a universal symmetry factor 4. We use a scattering
approach based on random transfer matrices.Comment: 15 pages, written in plain TeX, Preprint OUTP-93-42S (University of
Oxford), to appear in Phys. Rev.
Universal Quantum Signatures of Chaos in Ballistic Transport
The conductance of a ballistic quantum dot (having chaotic classical dynamics
and being coupled by ballistic point contacts to two electron reservoirs) is
computed on the single assumption that its scattering matrix is a member of
Dyson's circular ensemble. General formulas are obtained for the mean and
variance of transport properties in the orthogonal (beta=1), unitary (beta=2),
and symplectic (beta=4) symmetry class. Applications include universal
conductance fluctuations, weak localization, sub-Poissonian shot noise, and
normal-metal-superconductor junctions. The complete distribution P(g) of the
conductance g is computed for the case that the coupling to the reservoirs
occurs via two quantum point contacts with a single transmitted channel. The
result P(g)=g^(-1+beta/2) is qualitatively different in the three symmetry
classes. ***Submitted to Europhysics Letters.****Comment: 4 pages, REVTeX-3.0, INLO-PUB-94032
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