151 research outputs found
Superconductivity without attraction in a quasi-one-dimensional metal
An array of one-dimensional conductors coupled by transverse hopping and
interaction is studied with the help of a variational wave function. This wave
function is devised as to account for one-dimensional correlation effects. We
show that under broad conditions our system possesses the superconducting
ground state even if no attraction is present. The superconducting mechanism is
of many-body nature and deviates substantially from BCS. The phase diagram of
the model is mapped. It consists of two ordered phases competing against each
other: density wave, spin or charge, and unconventional superconductivity.
These phases are separated by the first order transition. The symmetry of the
superconducting order parameter is a non-universal property. It depends on
particulars of the Hamiltonian. Within the framework of our model possible
choices are the triplet -wave and the singlet -wave. Organic
quasi-one-dimensional superconductors have similar phase diagram.Comment: 12 pages, 2 Encapsulated PostScript figures, revtex4; the model's
Hamiltonian is revised as compared to previous version, this revision affects
prediction of the order parameter symmetr
Correlations in Chaotic Eigenfunctions at Large Separation
An energy eigenfunction in a classically chaotic system is known to have
spatial correlations which (in the limit of small ) are governed by a
microcanonical distribution in the classical phase space. This result is valid,
however, only over coordinate distances which are small compared to any
relevant classical distance scales (such as the cyclotron radius for a charged
particle in a magnetic field). We derive a modified formula for the correlation
function in the regime of large separation. This then permits a complete
description, over all length scales, of the statistical properties of chaotic
eigenfunctions in the limit. Applications to quantum dots are
briefly discussed.Comment: 8 pages, 1 figure, RevTeX, eps
Competition between different order parameters in a quasi-one-dimensional superconductor
We show that, under rather general assumptions, the phase diagram of a
quasi-one-dimensional repulsive Fermi system consists of two ordered phases:
the density wave, spin or charge, and the superconductivity. It is demonstrated
that the symmetry of the superconducting order parameter is a non-universal
property sensitive to microscopic details of the model. Three potentially
stable superconducting states are identified: they are triplet -wave,
singlet -wave, and -wave. Presence of multiple competing
superconducting states implies that for a real material this symmetry is
difficult to predict theoretically and hard to probe experimentally, since
artifacts of theoretical approximations or variations in experimental
conditions could tip the balance between the superconducting phases.Comment: 6 pages, 1 eps figur
Eigenfunctions of electrons in weakly disordered quantum dots: Crossover between orthogonal and unitary symmetries
A one-parameter random matrix model is proposed for describing the statistics
of the local amplitudes and phases of electron eigenfunctions in a mesoscopic
quantum dot in an arbitrary magnetic field. Comparison of the statistics
obtained with recent results derived from first principles within the framework
of supersymmetry technique allows to identify a transition parameter with real
microscopic characteristics of the problem. The random-matrix model is applied
to the statistics of the height of the resonance conductance of a quantum dot
in the regime of the crossover between orthogonal and unitary symmetry classes.Comment: 6 pages (latex), 3 figures available upon request, to appear in
Physical Review
Irradiation-induced confinement in a quasi-one-dimensional metal
The anisotropic resistivity of PrBaCuO has been measured as a
function of electron irradiation fluence. Localization effects are observed for
extremely small amounts of disorder corresponding to electron mean-free-paths
of order 100 unit cells. Estimates of the localization corrections suggest that
this anomalous localization threshold heralds a crossover to a ground state
with pronounced one-dimensional character in which conduction electrons become
confined to a small cluster of chains.Comment: 4 pages, 4 figure
Correlations due to localization in quantum eigenfunctions of disordered microwave cavities
Non-universal correlations due to localization are observed in statistical
properties of experimental eigenfunctions of quantum chaotic and disordered
microwave cavities. Varying energy {E} and mean free path {l} enable us to
experimentally tune from localized to delocalized states. Large level-to-level
Inverse Participation Ratio (IPR I_{2}) fluctuations are observed for the
disordered billiards, whose distribution is strongly asymmetric about .
The density auto-correlations of eigenfunctions are shown to decay
exponentially and the decay lengths are experimentally determined. All the
results are quantitatively consistent with calculations based upon nonlinear
sigma-models.Comment: 4 pages, LaTex, 5 .jpg figures. This paper with 5 embedded postscript
figures available (PS,PDF) at http://sagar.physics.neu.edu/preprints
Low-temperature conductivity of quasi-one-dimensional conductors: Luttinger liquid stabilized by impurities
A new non-Fermi-liquid state of quasi-one-dimensional conductors is suggested
in which electronic system exists in a form of collection of bounded Luttinger
liquids stabilized by impurities. This state is shown to be stable towards
interchain electron hopping at low temperatures. Electronic spectrum of the
system contains zero modes and collective excitations of the bounded Luttinger
liquids in the segments between impurities. Zero modes give rise to randomly
distributed localized electronic levels, and long-range interaction generates
the Coulomb gap in the density of states at the Fermi energy. Mechanism of
conductivity at low temperatures is phonon-assisted hopping via zero-mode
states. At higher voltages the excitations of Luttinger liquid are involved in
electron transport, and conductivity obeys power-law dependence on voltage. The
results provide a qualitative explanation for recent experimental data for
NbSe3 and TaS3 crystals.Comment: 12 pages, 1 figur
Possible co-existence of local itinerancy and global localization in a quasi-one-dimensional conductor
In the chain compound PrBaCuO localization appears simultaneously
with a dimensional crossover in the electronic ground state when the scattering
rate in the chains exceeds the hopping rate between the chains. Here we report
the discovery of a large, transverse magnetoresistance in PrBaCuO
in the localized regime. This result suggests a novel form of localization
whereby electrons retain their metallic (quasi-one-dimensional) character over
a microscopic length scale despite the fact that macroscopically, they exhibit
localized (one-dimensional) behavior.Comment: 4 pages, 4 Figure
Distribution of the Absorption by Chaotic States in Quantum Dots
The mesoscopic fluctuations of the absorption at optical transitions from a
low energy regular state to high energy chaotic states in an aggregate of
semiconductor quantum dots is studied. We provide a universal dependence of the
distribution of the absorption coefficient on the total number of dots and the
ratio of the level broadening to the level spacing. The distribution remain
broad even at large broadening, and the absorption spectrum should demonstrate
a strong sensitivity to weak magnetic field in the region of large and weak
absorption. The results can also apply to the absorption of Rydberg atoms in
strong magnetic field at the pre-threshold ionization.Comment: 4 pages, 2 eps figures, REVTeX3 + multicol.sty + epsf.te
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