86 research outputs found
Effect of a lattice upon an interacting system of electrons: Breakdown of scaling and decay of persistent currents
For an interacting system of N electrons, we study the conditions under which
a lattice model of size L with nearest neighbor hopping t and U/r Coulomb
repulsion has the same ground state as a continuum model. For a fixed value of
N, one gets identical results when the inter-electron spacing to the Bohr
radius ratio r_s < r_s^*. Above r_s^*, the persistent current created by an
enclosed flux begins to decay and r_s ceases to be the scaling parameter. Three
criteria giving similar r_s^* are proposed and checked using square lattices.Comment: 7 pages, 5 postscript figure
The optical conductivity of the quasi one-dimensional conductors: the role of forward scattering by impurities
We calculate the average conductivity sigma (omega) of interacting electrons
in one dimension in the presence of a long-range random potential (forward
scattering disorder). Taking the curvature of the energy dispersion into
account, we show that weak disorder leads to a transport scattering rate that
vanishes as omega^2 for small frequency omega. This implies that the real part
of the conductivity remains finite for omega -> 0, while the imaginary part
diverges. These effects are lost within the usual bosonization approach, which
relies on the linearization of the energy dispersion. We discuss our result in
the light of a recent experiment.Comment: 5 RevTex pages; more careful comparison with experiments and
discussion of interchain hopping added; some references added; to appear in
Phys. Rev.
Zn-doping effect on the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals
We report the magnetotransport properties of
Bi_{2}Sr_{2-x}La_{x}Cu_{1-z}Zn_{z}O_{6+\delta} (Zn-doped BSLCO) single crystals
with z of up to 2.2%. Besides the typical Zn-doping effects on the in-plane
resistivity and the Hall angle, we demonstrate that the nature of the
low-temperature normal state in the Zn-doped samples is significantly altered
from that in the pristine samples under high magnetic fields. In particular, we
observe nearly-isotropic negative magnetoresistance as well as an increase in
the Hall coefficient at very low temperatures in non-superconducting Zn-doped
samples, which we propose to be caused by the Kondo scattering from the local
moments induced by Zn impurities.Comment: 4 pages, 4 figures, final version (one reference added), published in
Phys. Rev.
Short Range Interaction Effects on the Density of States of Disordered Two Dimensional Crystals with a half--filled band
The Density of electronic States (DoS) of a two--dimensional square lattice
with substitutional impurities is calculated in the presence of short--range
electron--electron interactions. In the middle of the energy band, the Bragg
reflections off the Brillouin zone boundary are shown to lead to additional
quantum corrections to the DoS, the sign of which is opposite to the sign of
the Altshuler--Aronov's logarithmic correction. The resulting quantum
correction to the DoS at half--filling is positive, i.e. the DoS increases
logarithmically as the Fermi energy is approached. However, far from the
commensurate points where the Bragg reflections are suppressed, the negative
logarithmic corrections to the DoS survive.Comment: 5 pages 2 figure
Quantum Breathers in a Nonlinear Lattice
We study nonlinear phonon excitations in a one-dimensional quantum nonlinear
lattice model using numerical exact diagonalization. We find that multi-phonon
bound states exist as eigenstates which are natural counterparts of breather
solutions of classical nonlinear systems. In a translationally invariant
system, these quantum breather states form particle-like bands and are
characterized by a finite correlation length. The dynamic structure factor has
significant intensity for the breather states, with a corresponding quenching
of the neighboring bands of multi-phonon extended states.Comment: 4 pages, RevTex, 4 postscript figures, Physical Relview Letters (in
press
Evidence for strong electron-phonon coupling and polarons in the optical response of La_{2-x}Sr_xCuO_4
The normal state optical response of La_{2-x}Sr_xCuO_4 is found to be
consistent with a simple multi-component model, based on free carriers with
strong electron-phonon interaction, localized polaronic states near 0.15 eV and
a mid-infrared band at 0.5 eV. Normal state reflectance and absorbance of
La_{1.83}Sr_{0.17}CuO_4 are investigated and their temperature dependence is
explained. Both, the ac and dc response are recovered and the quasi-linear
behavior of the optical scattering rate up to 3000- 4000 cm^{-1} is found to be
consistent with strong electron-phonon interaction, which also accounts for the
value of T_c. Although not strictly applicable in the superconducting state,
our simple model accounts for the observed penetration depth and the optical
response below T_c can be recovered by introducing a small amount of additional
carriers. Our findings suggest that the optical response of La_{2-x}Sr_xCuO_4
could be explained both, in the normal and superconducting state, by a simple
multi-fluid model with strong electron-phonon interaction if the gap symmetry
and the temperature dependence of the 0.5 eV mid-infrared band are adequately
taken into account.Comment: 22 pages, REVTeX, 12 figures in ps-fil
Critical temperature of the superfluid transition in bose liquids
A phenomenological criterion for the superfluid transition is proposed, which
is similar to the Lindemann criterion for the crystal melting. Then we derive a
new formula for the critical temperature, relating to the mean
kinetic energy per particle above the transition. The suppression of the
critical temperature in a sufficiently dense liquid is described as a result of
the quantum decoherence phenomenon. The theory can account for the observed
dependence of on density in liquid helium and results in an
estimate K for molecular hydrogen.Comment: 4 pages, 1 fi
Superconductivity in the Pseudogap State due to Fluctuations of Short-Range Order
We analyze the anomalies of superconducting state (s and d-wave pairing) in a
simple model of pseudogap state, induced by fluctuations of short - range order
(e.g. antiferromagnetic), based on the model Fermi surface with "hot patches".
We derive a system of recursion relations for Gorkov's equations which take
into account all diagrams of perturbation theory for electron interaction with
fluctuations of short-range order. Then we find superconducting transition
temperature and gap behavior for different values of the pseudogap width and
correlation lengths of short-range order fluctuations. In a similar
approximation we derive the Ginzburg-Landau expansion and study the main
physical characteristics of a superconductor close to the transition
temperature, both as functions of the pseudogap width and correlation length of
fluctuations. Results obtained are in qualitative agreement with a number of
experiments on underdoped HTSC-cuprates.Comment: 18 pages, 12 figures, RevTeX 3.0, minor misprints corrected, to
appear in JET
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