180 research outputs found
Doping induced inhomogeneity in high-Tc superconductors
Doping and disorder are inseparable in the superconducting cuprates. Assuming
the simplest possible disordered doping, we construct a semiphenomenological
model and analyze its experimental consequences. Among the affected
experimental quantities are the ARPES spectra and thermodynamic properties.
From our model we make a prediction for the width of the local
superconducting gap distribution with the only experimentally unknown parameter
being the superconducting correlation length. Thus, our model provides a direct
way of determining the superconducting correlation length from a known
experimental gap distribution.Comment: 5 pages, 3 eps figures. Expanded version of talk presented by AVB at
the ISS 2000, Oct 14-16, Tokyo, Japa
Wiedza osobista dziecka w świadomości i działaniach praktycznych nauczycieli. Recenzja monografii Ewy Kochanowskiej (2018), Wiedza osobista dziecka w refleksji i praktyce nauczycieli edukacji wczesnoszkolnej, Kraków: Oficyna Wydawnicza Impuls.
A possible explanation of the phase diagram of cuprate superconductors
A d-p pairing curve that is consistent with the pseudogap curve observed in
experiments is found on a d-p model on phonon mechanism. On the discovery we
suggest that there are two pseudogaps associated with the nearly localized d-p
pairs and nearly free p-p pairs. The p-p pairs look like bosons and are
responsible for superconductivities.Comment: 6 pages, 3 figure
Electronic Theory for Bilayer-Effects in High-T_c Superconductors
The normal and the superconducting state of two coupled CuO_2 layers in the
High-T_c superconductors are investigated by using the bilayer Hubbard model,
the FLEX approximation on the real frequency axis and the Eliashberg theory. We
find that the planes are antiferromagnetically correlated which leads to a
strongly enhanced shadow band formation. Furthermore, the inter-layer hopping
is renormalized which causes a blocking of the quasi particle inter-plane
transfer for low doping concentrations. Finally, the superconducting order
parameter is found to have a d_{x^2-y^2} symmetry with significant additional
inter-layer contributions.Comment: 5 pages, Revtex, 4 postscript figure
Luttinger theorem for a spin-density-wave state
We obtained the analog of the Luttinger relation for a commensurate
spin-density-wave state. We show that while the relation between the area of
the occupied states and the density of particles gets modified in a simple and
predictable way when the system becomes ordered, a perturbative consideration
of the Luttinger theorem does not work due to the presence of an anomaly
similar to the chiral anomaly in quantum electrodynamics.Comment: 4 pages, RevTeX, 1 figure embedded in the text, ps-file is also
available at http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm
Commensurate and Incommensurate Spin Fluctuations in YBa_2Cu_3O_{6+y}
We present an interpretation of the recent neutron data on the commensurate
and incommensurate spin fluctuations found in YBa_2d$Cu_3O_{6+y} based on a
special configuration of the electronic dispersion and intervention from the
d_{x^2-y^2}-wave superconducting phase. The observed switch over between the
commensurate and incommensurate fluctuation spectra at the change of frequency
or temperature is naturally accounted within this scenario.Comment: 4 pages and 4 fig
Low temperature thermodynamics of charged bosons in a random potential and the specific heat of La_{2-x}Sr_{x}CuO_{4} below Tc
We propose a simple analytical form of the partition function for charged
bosons localised in a random potential and derive the consequent thermodynamics
below the superfluid transition temperature. In the low temperature limit, the
specific heat, C, depends on the localisation length exponent nu: C is linear
for nu1 we find C proportional to T^{1/nu}. This unusual
sub-linear temperature dependence of the specific heat has recently been
observed in La_{2-x}Sr_{x}CuO_{4} below Tc.Comment: Revtex, 6 pages, 4 postscript figure
On the vertex corrections in antiferromagnetic spin fluctuation theories
We argue that recent calculations by Amin and Stamp (PRL 77, 301 (1996);
cond-mat/9601086) overestimate the strength of the vertex corrections in the
spin-fermion model for cuprates. We clarify the physical origin of the apparent
discrepancy between their results and earlier calculations. We also comment on
the relative sign of the vertex correction.Comment: 3 pages, Revtex, 1 figure, ps-file also available at
http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm
Normal-state pseudogap and electron flat dispersion in copper oxide materials
The anomalous momentum and doping dependence of the electron spectral
function and electron dispersion for copper oxide materials in the underdoped
regime are studied within the t-J model. It is shown that the electron spectrum
is changed with dopings, and the electron dispersion exhibits a flat band
around (,0) point in the Brillouin zone, which leads to the normal-state
pseudogap formation. The theoretical results are consistent with the
experiments and numerical simulations.Comment: 13 pages, Latex, Two figures are included, accepted for publication
in Phys. Lett.
Quasiparticle dispersion of the t-J and Hubbard models
The spectral weight of the two dimensional and Hubbard models has been calculated using exact diagonalization and
quantum Monte Carlo techniques, at several densities . The photoemission region contains two
dominant distinct features, namely a low-energy quasiparticle peak with
bandwidth of order J, and a broad valence band peak at energies of order t.
This behavior away from half-filling, as long as the
antiferromagnetic (AF) correlations are robust. The results give support to
theories of the copper oxide materials based on the behavior of holes in
antiferromagnets, and it also provides theoretical guidance for the
interpretation of experimental photoemission data for the cuprates.Comment: (minor changes) RevTeX, 4 figures available on reques
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