83 research outputs found
Marginal Fermi Liquid with a Two-Dimensional Patched Fermi Surface
We consider a model composed of Landau quasiparticle states with patched
Fermi surfaces (FS) sandwiched by states with flat FS to simulate the ``cold''
spot regions in cuprates. We calculate the one particle irreducible function
and the self-energy up to two-loop order. Using renormalization group arguments
we show that in the forward scattering channel the renormalized coupling
constant is never infrared stable due to the flat FS sectors. Furthemore we
show that the self-energy scales with energy as as , and thus the Fermi liquid state within each FS
patch is turned into a marginal Fermi liquid.Comment: 5 pages, 3 ps figure
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
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
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
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
Optical Conductivity in a Simple Model of Pseudogap State in Two-Dimensional System
We present calculation of optical conductivity in a simple model of
electronic spectrum of two-dimensional system with "hot patches" on the Fermi
surface, leading to non Fermi-liquid renormalization of the spectral density
(pseudogap) on these patches. It is shown that this model qualitatively
reproduces basic anomalies of optical experiments in the pseudogap state of
copper oxides.Comment: 12 pages, 6 figures, RevTeX 3.0, Postscript figures attache
Nesting Induced Precursor Effects: a Renormalization Group Approach
We develop a controlled weak coupling renormalization group (RG) approach to
itinerant electrons. Within this formalism we rederive the phase diagram for
two-dimensional (2D) non-nested systems. Then we study how nesting modifies
this phase diagram. We show that competition between p-p and p-h channels,
leads to the manifestation of unstable precursor fixed points in the RG flow.
This effect should be experimentally measurable, and may be relevant for an
explanation of pseudogaps in the high temperature superconductors (HTC), as a
crossover phenomenon.Comment: 4 pages, 4 figures, 1 tabl
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
Instructions for Laboratory Training in General Microbiology & Immunology for Students of Medical Faculty (English Medium)
LABORATORY TRAININGGENERAL MICROBIOLOGYIMMUNOLOGYИНОСТРАННЫЕ СТУДЕНТЫЛАБОРАТОРНЫЕ ЗАНЯТИЯМИКРОБИОЛОГИЯАЛЛЕРГОЛОГИЯ И ИММУНОЛОГИЯInstructions for laboratory training in General Microbiology and Immunology for students of the faculty of General Medicine were compiled according to basic educational plan and program, approved by Ministry of Health Care of Republic of Belarus. The plan, schedule of laboratory training and basic practical skills in general microbiology and immunology are presented in this workbook. The instructions are prepared for medical students of higher educational establishments. Инструкция по проведению лабораторных занятий по общей микробиологии и иммунологии для студентов лечебного факультета составлена по основному учебному плану и программе, утвержденным Министерством здравоохранения Республики Беларусь. План, график лабораторных занятий и основные практические навыки по общей микробиологии и иммунологии представлены в данной рабочей тетради
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