26 research outputs found
Two-fluid behavior of the Kondo lattice in the 1/N slave boson approach
It has been recently shown by Nakatsuji, Pines, and Fisk [S. Nakatsuji, D.
Pines, and Z. Fisk, Phys. Rev. Lett. 92, 016401 (2004)] from the
phenomenological analysis of experiments in Ce1-xLaxCoIn5 and CeIrIn5 that
thermodynamic and transport properties of Kondo lattices below coherence
temperature can be very successfully described in terms of a two-fluid model,
with Kondo impurity and heavy electron Fermi liquid contributions. We analyze
thermodynamic properties of Kondo lattices using 1/N slave boson treatment of
the periodic Anderson model and show that these two contributions indeed arise
below the coherence temperature. We find that the Kondo impurity contribution
to thermodynamics corresponds to thermal excitations into the flat portion of
the energy spectrum.Comment: 7 pages, 2 figure
Finite-size scaling for the S=1/2 Heisenberg Antiferromagnetic Chain
Corrections to the asymptotic correlation function in a Heisenberg spin-1/2
antiferromagnetic spin chain are known to vanish slowly (logarithmically) as a
function of the distance r or the chain size L. This leads to significant
differences with numerical results. We calculate the sub-leading logarithmic
corrections to the finite-size correlation function, using renormalization
group improved perturbation theory, and compare the result with numerical data.Comment: 7 pages Revtex, 3 figure
Coherent transport and nonlocality in mesoscopic SNS junctions: anomalous magnetic interference patterns
We show that in {\em ballistic} mesoscopic SNS junctions the period of
critical current vs. magnetic flux dependence (magnetic interference pattern),
, changes {\em continuously and non-monotonically} from to
as the length-to-width ratio of the junction grows, or temperature
drops. In {\em diffusive} mesoscopic junctions the change is even more drastic,
with the first zero of appearing at .
The effect is a manifestation of nonlocal relation between the supercurrent
density and superfluid velocity in the normal part of the system, with the
characteristic scale (ballistic limit) or
(diffusive limit), the normal metal
coherence length, and arises due to restriction of the quasiparticle phase
space near the lateral boundaries of the junction. It explains the
-periodicity recently observed by Heida et al. (Phys. Rev. B {\bf 57},
R5618 (1998)). We obtained explicit analytical expressions for the magnetic
interference pattern for a junction with an arbitrary length-to-width ratio.
Experiments are proposed to directly observe the - and
-transitions.Comment: 13 pages, 7 figures. New results on diffusive mesoscopic SNS
junctions included. Typo in Eq.(27) corrected. Contribution to the special
issue of Superlattices and Microstructures on mesoscopic superconductivit
Phenomenological model of protected behavior in the cuprate superconductors
By extending previous work on the scaling of low frequency magnetic
properties of the 2-1-4 cuprates to the 1-2-3 materials, we arrive at a
consistent phenomenological description of protected behavior in the pseudogap
state of the magnetically underdoped cuprates. Between zero hole doping and a
doping level of it reflects the presence of a mixture of an
insulating spin liquid that produces the measured magnetic scaling behavior and
a Fermi liquid that becomes superconducting for doping levels . Our
analysis suggests the existence of two quantum critical points, at doping
levels, and , and that d-wave superconductivity in
the pseudogap region arises from quasiparticle-spin liquid interaction, i.e.
magnetic interactions between quasiparticles in the Fermi liquid induced by
their coupling to the spin liquid excitations.Comment: 4 pages, 4 figure
Universal Behavior and the Two-component Character of Magnetically Underdoped Cuprate Superconductors
We present a detailed review of scaling behavior in the magnetically
underdoped cuprate superconductors (hole dopings less than 0.20) and show that
it reflects the presence of two coupled components throughout this doping
regime: a non-Landau Fermi liquid and a spin liquid whose behavior maps onto
the theoretical Monte Carlo calculations of the 2D Heisenberg model of
localized Cu spins for most of its temperature domain. We use this mapping to
extract the doping dependence of the strength, of the spin liquid
component and the effective interaction, J_eff(x) between the remnant localized
spins that compose it; we find both decrease linearly with x as the doping
level increases. We discuss the physical origin of pseudogap behavior and
conclude that it is consistent with scenarios in which the both the large
energy gaps found in the normal state and their subsequent superconductivity
are brought about by the coupling between the Fermi liquid quasiparticles and
the spin liquid excitations, and that differences in this coupling between the
1-2-3 and 2-1-4 materials can explain the measured differences in their
superconducting transition temperatures and other properties.Comment: 80 pages, 43 figure
Impurity correlations in dilute Kondo alloys
The single impurity Kondo model is often used to describe metals with dilute
concentrations (n_i) of magnetic impurities. Here we examine how dilute the
impurities must be for this to be valid by developing a virial expansion in
impurity density. The O(n_i^2) term is determined from results on the
2-impurity Kondo problem by averaging over the RKKY coupling. The non-trivial
fixed point of the 2-impurity problem could produce novel singularities in the
heat capacity of dilute alloys at O(n_i^2).Comment: 6 pages, no figure