484 research outputs found
P-wave Pairing and Colossal Magnetoresistance in Manganese Oxides
We point out that the existing experimental data of most manganese oxides
show the {\sl frustrated} p-wave superconducting condensation in the
ferromagnetic phase in the sense that the superconducting coherence is not long
enough to cover the whole system. The superconducting state is similar to the
state in superfluid He-3. The sharp drop of resistivity, the steep jump
of specific heat, and the gap opening in tunneling are well understood in terms
of the p-wave pairing. In addition, colossal magnetoresistance (CMR) is
naturally explained by the superconducting fluctuations with increasing
magnetic fields. The finite resistivity may be due to some magnetic
inhomogeneities. This study leads to the possibility of room temperature
superconductivity.Comment: LaTex, 14 pages, For more information, please send me an e-mail.
e-mail adrress : [email protected]
Thermoelectric Flux in Superconducting Rings
Definitive measurements by Van Harlingen et al. in 1980 show that the flux induced by a temperature difference across the two junctions of a Pb-In ring exceeds theoretical expectation by a factor, ϳ105. The theory fails owing to ͑mis͒use of a Boltzmann transport equation to describe the thermal diffusion of quasi-particle excitations, a treatment which violates electron conservation. An electron-conserving transport theory is developed and explains the data
Properties of short-range and long-range correlation energy density functionals from electron-electron coalescence
The combination of density functional theory with other approaches to the
many-electron problem through the separation of the electron-electron
interaction into a short-range and a long-range contribution is a promising
method, which is raising more and more interest in recent years. In this work
some properties of the corresponding correlation energy functionals are derived
by studying the electron-electron coalescence condition for a modified
(long-range-only) interaction. A general relation for the on-top (zero
electron-electron distance) pair density is derived, and its usefulness is
discussed with some examples. For the special case of the uniform electron gas,
a simple parameterization of the on-top pair density for a long-range only
interaction is presented and supported by calculations within the ``extended
Overhauser model''. The results of this work can be used to build
self-interaction corrected short-range correlation energy functionals.Comment: revised version, to appear in Phys. Rev.
System-adapted correlation energy density functionals from effective pair interactions
We present and discuss some ideas concerning an ``average-pair-density
functional theory'', in which the ground-state energy of a many-electron system
is rewritten as a functional of the spherically and system-averaged pair
density. These ideas are further clarified with simple physical examples. We
then show that the proposed formalism can be combined with density functional
theory to build system-adapted correlation energy functionals. A simple
approximation for the unknown effective electron-electron interaction that
enters in this combined approach is described, and results for the He series
and for the uniform electron gas are briefly reviewed.Comment: to appear in Phil. Mag. as part of Conference proceedings for the
"Electron Correlations and Materials Properties", Kos Greece, July 5-9, 200
Broken Symmetry in Density-Functional Theory: Analysis and Cure
We present a detailed analysis of the broken-symmetry mean-field solutions
using a four-electron rectangular quantum dot as a model system. Comparisons of
the density-functional theory predictions with the exact ones show that the
symmetry breaking results from the single-configuration wave function used in
the mean-field approach. As a general cure we present a scheme that
systematically incorporates several configurations into the density-functional
theory and restores the symmetry. This cure is easily applicable to any
density-functional approach.Comment: 4 pages, 4 figures, submitted to PR
A chiral crystal in cold QCD matter at intermediate densities?
The analogue of Overhauser (particle-hole) pairing in electronic systems
(spin-density waves with non-zero total momentum ) is analyzed in
finite-density QCD for 3 colors and 2 flavors, and compared to the
color-superconducting BCS ground state (particle-particle pairing, =0). The
calculations are based on effective nonperturbative four-fermion interactions
acting in both the scalar diquark as well as the scalar-isoscalar quark-hole
('') channel. Within the Nambu-Gorkov formalism we set up the coupled
channel problem including multiple chiral density wave formation, and evaluate
the resulting gaps and free energies. Employing medium-modified
instanton-induced 't Hooft interactions, as applicable around
GeV (or 4 times nuclear saturation density), we find the 'chiral crystal phase'
to be competitive with the color superconductor.Comment: 14 pages ReVTeX, including 11 ps-/eps-figure
Evidence for an antiferromagnetic component in the magnetic structure of ZrZn2
Zero-field muon spin rotation experiments provide evidence for an
antiferromagnetic component in the magnetic structure of the intermetallics
ZrZn2.Comment: 5 pages, 2 figure
Experimental Implementation of Logical Bell State Encoding
Liquid phase NMR is a general purpose test-bed for developing methods of
coherent control relevant to quantum information processing. Here we extend
these studies to the coherent control of logical qubits and in particular to
the unitary gates necessary to create entanglement between logical qubits. We
report an experimental implementation of a conditional logical gate between two
logical qubits that are each in decoherence free subspaces that protect the
quantum information from fully correlated dephasing.Comment: 9 Pages, 5 Figure
Ground-state densities and pair correlation functions in parabolic quantum dots
We present an extensive comparative study of ground-state densities and pair
distribution functions for electrons confined in two-dimensional parabolic
quantum dots over a broad range of coupling strength and electron number. We
first use spin-density-functional theory to determine spin densities that are
compared with Diffusion Monte Carlo (DMC) data. This accurate knowledge of
one-body properties is then used to construct and test a local approximation
for the electron-pair correlations. We find very satisfactory agreement between
this local scheme and the available DMC data, and provide a detailed picture of
two-body correlations in a coupling-strength regime preceding the formation of
Wigner-like electron ordering.Comment: 18 pages, 12 figures, submitte
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