1,437 research outputs found
Dispersion relations and speeds of sound in special sectors for the integrable chain with alternating spins
Based on our previous analysis \cite{doerfel3} of the anisotropic integrable
chain consisting of spins and we compare the dispersion relations
for the sectors with infinite Fermi zones. Further we calculate the speeds of
sound for regions close to sector borders, where the Fermi radii either vanish
or diverge, and compare the results.Comment: 11 pages, LaTeX2e, uses iopart.cls,graphicx.sty and psfrag.sty, 2
figure
Conductance length autocorrelation in quasi one-dimensional disordered wires
Employing techniques recently developed in the context of the Fokker--Planck
approach to electron transport in disordered systems we calculate the
conductance length correlation function
for quasi 1d wires. Our result is valid for arbitrary lengths L and .
In the metallic limit the correlation function is given by a squared
Lorentzian. In the localized regime it decays exponentially in both L and
. The correlation length is proportional to L in the metallic regime
and saturates at a value approximately given by the localization length
as .Comment: 23 pages, Revtex, two figure
Analytical Results for Random Band Matrices with Preferential Basis
Using the supersymmetry method we analytically calculate the local density of
states, the localiztion length, the generalized inverse participation ratios,
and the distribution function of eigenvector components for the superposition
of a random band matrix with a strongly fluctuating diagonal matrix. In this
way we extend previously known results for ordinary band matrices to the class
of random band matrices with preferential basis. Our analytical results are in
good agreement with (but more general than) recent numerical findings by
Jacquod and Shepelyansky.Comment: 8 pages RevTex and 1 Figure, both uuencode
--Oscillations for Correlated Electron Pairs in Disordered Mesoscopic Rings
The full spectrum of two interacting electrons in a disordered mesoscopic
one--dimensional ring threaded by a magnetic flux is calculated numerically.
For ring sizes far exceeding the one--particle localization length we
find several --periodic states whose eigenfunctions exhibit a pairing
effect. This represents the first direct observation of interaction--assisted
coherent pair propagation, the pair being delocalized on the scale of the whole
ring.Comment: 4 pages, uuencoded PostScript, containing 5 figures
Complete phase diagram for the integrable chain with alternating spins in the sectors with competing interactions
We investigate the anisotropic integrable spin chain consisting of spins
and by means of thermodynamic Bethe ansatz for the anisotropy
, where the analysis of the Takahashi conditions leads to a more
complicated string picture. We give the phase diagram with respect to the two
real coupling constants and , which contains a new region
where the ground state is formed by strings with infinite Fermi zones. In this
region the velocities of sound for the two physical excitations have been
calculated from the dressed energies. This leads to an additional line of
conformal invariance not known before.Comment: 13 pages, LaTeX, uses ioplppt.sty and epsfig.sty, figure 3 correcte
Localization in a rough billiard: A sigma model formulation
We consider the quantum dynamics of a particle in a weakly rough billiard.
The Floquet operator for reflection at the boundary is obtained as a unitary
band matrix. The resulting dynamics in angular momentum space can be treated in
the framework of the one-dimensional supersymmetric nonlinear sigma model. We
find analytically localization and the corresponding localization length
where is the classical diffusion constant due to boundary
scattering.Comment: 4 pages, Revtex, no figures, to appear in Phys. Rev. B, Rapid
Communication
Properties of the chiral spin liquid state in generalized spin ladders
We study zero temperature properties of a system of two coupled quantum spin
chains subject to fields explicitly breaking time reversal symmetry and parity.
Suitable choice of the strength of these fields gives a model soluble by Bethe
Ansatz methods which allows to determine the complete magnetic phase diagram of
the system and the asymptotics of correlation functions from the finite size
spectrum. The chiral properties of the system for both the integrable and the
nonintegrable case are studied using numerical techniques.Comment: 19 pages, 9eps figures, Late
Emergence of Quantum Ergodicity in Rough Billiards
By analytical mapping of the eigenvalue problem in rough billiards on to a
band random matrix model a new regime of Wigner ergodicity is found. There the
eigenstates are extended over the whole energy surface but have a strongly
peaked structure. The results of numerical simulations and implications for
level statistics are also discussed.Comment: revtex, 4 pages, 4 figure
Unexpected systematic degeneracy in a system of two coupled Gaudin models with homogeneous couplings
We report an unexpected systematic degeneracy between different multiplets in
an inversion symmetric system of two coupled Gaudin models with homogeneous
couplings, as occurring for example in the context of solid state quantum
information processing. We construct the full degenerate subspace (being of
macroscopic dimension), which turns out to lie in the kernel of the commutator
between the two Gaudin models and the coupling term. Finally we investigate to
what extend the degeneracy is related to the inversion symmetry of the system
and find that indeed there is a large class of systems showing the same type of
degeneracy.Comment: 13 pages, 4 figure
Effective Model Formulation for Two Interacting Electrons in a Disordered Metal
We derive an analytical theory for two interacting electrons in a
--dimensional random potential. Our treatment is based on an effective
random matrix Hamiltonian. After mapping the problem on a nonlinear
model, we exploit similarities with the theory of disordered metals to identify
a scaling parameter, investigate the level correlation function, and study the
transport properties of the system. In agreement with recent numerical work we
find that pair propagation is subdiffusive and that the pair size grows
logarithmically with time.Comment: 4 pages, revtex, no figure
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