106 research outputs found
Magnetoresistance of YBa2Cu3O7 in the "cold spots" model
We calculate the in-plane magnetoresistance of
YBaCuO in a magnetic field applied perpendicular to the
planes for the ``cold spots'' model. In this model, the electron relaxation
time at small regions on the Fermi surface near the
Brillouin zone diagonals is much longer than the relaxation time
at the rest of the Fermi surface ( is temperature). In
qualitative agreement with the experiment, we find that Kohler's rule is
strongly violated, but the ratio ,
where is the Hall angle, is approximately
temperature-independent. We find the ratio is about 5.5, which is of the same
order of magnitude as in the experiment.Comment: RevTeX, 4 pages, 6 figures. V.2: 2 references adde
Magnetooptical sum rules close to the Mott transition
We derive new sum rules for the real and imaginary parts of the
frequency-dependent Hall constant and Hall conductivity. As an example, we
discuss their relevance to the doped Mott insulator that we describe within the
dynamical mean-field theory of strongly correlated electron systems.Comment: 4 pages, 4 ps figures; accepted for publication in PR
Color Effects Associated with the 1999 Microlensing Brightness Peaks in Gravitationally Lensed Quasar Q2237+0305
Photometry of the Q2237+0305gravitational lens in VRI spectral bands with the
1.5-m telescope of the high-altitude Maidanak observatory in 1995-2000 is
presented. Monitoring of Q2237+0305 in July-October 2000, made at nearly daily
basis, did not reveal rapid (night-to-night and intranight) variations of
brightness of the components during this time period. Rather slow changes of
magnitudes of the components were observed, such as 0.08 mag fading of B and C
components and 0.05 mag brightening of D in R band during July 23 - October 7,
2000. By good luck three nights in 1999 were almost at the time of the strong
brightness peak of image C, and approximately in the middle of the ascending
slope of the image A brightness peak. The C component was the most blue one in
the system in 1998 and 1999, having changed its (V-I) color from 0.56 mag to
0.12 mag since August 1997, while its brightness increased almost 1.2 mag
during this time period. The A component behaved similarly between August 1998
and August 2000, having become 0.47 mag brighter in R, and at the same time,
0.15 mag bluer. A correlation between the color variations and variations of
magnitudes of the components is demonstrated to be significant and reaches
0.75, with a regression line slope of 0.33. A color (V-I) vrs color (V-R) plot
shows the components settled in a cluster, stretched along a line with a slope
of 1.31. Both slopes are noticeably smaller than those expected if a standard
galactic interstellar reddening law were responsible for the differences
between the colors of images and their variations over time. We attribute the
brightness and color changes to microlensing of the quasar's structure, which
we conclude is more compact at shorter wavelengths, as predicted by most quasar
models featuring an energizing central source.Comment: 14 pages, 7 figures, LaTeX, submitted to A&
Impurity and strain effects on the magnetotransport of La1.85Sr0.15Cu(1-y)Zn(y)O4 films
The influence of zinc doping and strain related effects on the normal state
transport properties(the resistivity, the Hall angle and the orbital magneto-
resistance(OMR) is studied in a series of La1.85Sr0.15Cu(1-y)Zn(y)O4 films with
values of y between 0 and 0.12 and various degrees of strain induced by the
mismatch between the films and the substrate. The zinc doping affects only the
constant term in the temperature dependence of cotangent theta but the strain
affects both the slope and the constant term, while their ratio remains
constant.OMR is decreased by zinc doping but is unaffected by strain. The ratio
delta rho/(rho*tan^2 theta) is T-independent but decreases with impurity
doping. These results put strong constraints on theories of the normal state of
high- temperature superconductors
Measuring anisotropic scattering in the cuprates
A simple model of anisotropic scattering in a quasi two-dimensional metal is
studied. Its simplicity allows an analytic calculation of transport properties
using the Boltzmann equation and relaxation time approximation. We argue that
the c-axis magnetoresistance provides the key test of this model of transport.
We compare this model with experiments on overdoped Tl-2201 and find reasonable
agreement using only weak scattering anisotropy. We argue that optimally doped
Tl-2201 should show strong angular-dependent magnetoresistance within this
model and would provide a robust way of determining the in-plane scattering
anisotropy in the cuprates.Comment: 12 pages, 8 figures, typset in REVTeX 4. Version 2; added references
and corrected typo
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
Infrared Hall effect in high Tc superconductors: Evidence for non-Fermi liquid Hall scattering
Infrared (20-120 cm-1 and 900-1100 cm-1) Faraday rotation and circular
dichroism are measured in high Tc superconductors using sensitive polarization
modulation techniques. Optimally doped YBCO thin films are studied at
temperatures down to 15 K and magnetic fields up to 8 T. At 1000 cm-1 the Hall
conductivity varies strongly with temperature in contrast to the longitudinal
conductivity which is nearly independent of temperature. The Hall scattering
rate has a T^2 temperature dependence but, unlike a Fermi liquid, depends only
weakly on frequency. The experiment puts severe constraints on theories of
transport in the normal state of high Tc superconductors.Comment: 8 pages, 3 figure
Ginzburg-Landau Expansion in a Toy Model of Superconductor with Pseudogap
We propose a toy model of electronic spectrum of two-dimensional system with
``hot-patches'' on the Fermi surface, which leads to essential renormalization
of spectral density (pseudogap). Within this model we derive Ginzburg-Landau
expansion for both s-wave and d-wave Cooper pairing and analyze the influence
of pseudogap formation on the basic properties of superconductors.Comment: 14 pages, 14 figures, RevTeX 3.0, Postscript figures attached, some
changes in the explanation of the model, published in JETP 115, No.2, (1999
Preparation of copper electrical engineering alloy strip with high service properties
Output is organized for industrial batches of electrical engineering strip with improved service properties, i.e., copper bus bars of rectangular section (σu determination is simplified and surface quality evaluation after bend testing is improved), commutator copper-cadmium strip of trapezoidal section (hardness increased, strip camber reduced, bulges and scratches absent from basic profile), and commutator copper-silver strip (electrical conductivity increased and stable mechanical properties achieved). © 2013 Springer Science+Business Media New York
Singularities in the optical response of cuprates
We argue that the detailed analysis of the optical response in cuprate
superconductors allows one to verify the magnetic scenario of superconductivity
in cuprates, as for strong coupling charge carriers to antiferromagnetic spin
fluctuations, the second derivative of optical conductivity should contain
detectable singularities at , , and
, where is the amplitude of the
superconducting gap, and is the resonance energy of spin
fluctuations measured in neutron scattering. We argue that there is a good
chance that these singularities have already been detected in the experiments
on optimally doped .Comment: 6 pages, 4 figure
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