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 ${\rm Re} \Sigma \sim \omega \ln \omega$ as $\omega \to 0$, and thus the Fermi liquid state within each FS patch is turned into a marginal Fermi liquid.Comment: 5 pages, 3 ps figure

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

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

Optical observations of SBS1520+530 at TUG

We present the light curves of the components of gravitationally lensed source SBS1520+530 in Rc band, obtained during the interval 2001-2005 with the 1.5 m Russian-Turkish Telescope RTT150 at TÜBITAK National Observatory of Turkey. The time delay of brightness fluctuations between the two components of the gravitationally double-imaged quasar corresponding to 2001-2002 period of observations is determined. Using all the available data, at least two microlensing events, one of them with long-time linear behavior and second one with duration of a few hundred days, are detected. © 2008 Springer-Verlag Berlin Heidelberg

Analysis of optical light curves for the components of the gravitationally lensed quasar SBS 1520+530 based on observations with the 1.5-m RTT-150 telescope in 2001-2005

We present the R c-band light curves for components A and B of the gravitationally lensed quasar SBS 1520+530 obtained during 2001-2005 with the 1.5-m Russian-Turkish Telescope (RTT-150) at the TUBITAK National Observatory (Turkey). Based on an analysis of the data for the period 2001-2002, we have estimated the time delay of the brightness fluctuations between components A and B of the quasar to be 128 days. This time delay agrees with its previously published values for the periods 1999-2001 and 2003-2004. Using all of the published data on the brightnesses of components A and B of SBS 1520+530 for the 6-year period, we have found at least two microlensing events. One event has the pattern of a long-term linear trend; the duration of the other event is several hundred days. © Pleiades Publishing, Inc., 2006

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

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

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

Possibility of long-range order in clean mesoscopic cylinders

A microscopic Hamiltonian of the magnetostatic interaction is discussed. This long-range interaction can play an important role in mesoscopic systems leading to an ordered ground state. The self-consistent mean field approximation of the magnetostatic interaction is performed to give an effective Hamiltonian from which the spontaneous, self-sustaining currents can be obtained. To go beyond the mean field approximation the mean square fluctuation of the total momentum is calculated and its influence on self-sustaining currents in mesoscopic cylinders with quasi-1D and quasi-2D conduction is considered. Then, by the use of the microscopic Hamiltonian of the magnetostatic interaction for a set of stacked rings, the problem of long-range order is discussed. The temperature $T^{*}$ below which the system is in an ordered state is determined.Comment: 14 pages, REVTeX, 5 figures, in print in Phys. Rev.

Magnetotransport in the Normal State of La1.85Sr0.15Cu(1-y)Zn(y)O4 Films

We have studied the magnetotransport properties in the normal state for a series of La1.85Sr0.15Cu(1-y)Zn(y)O4 films with values of y, between 0 and 0.12. A variable degree of compressive or tensile strain results from the lattice mismatch between the substrate and the film, and affects the transport properties differently from the influence of the zinc impurities. In particular, the orbital magnetoresistance (OMR) varies with y but is strain-independent. The relations for the resistivity and the Hall angle and the proportionality between the OMR and tan^2 theta are followed about 70 K. We have been able to separate the strain and impurity effects by rewriting the above relations, where each term is strain-independent and depends on y only. We also find that changes in the lattice constants give rise to closely the same fractional changes in other terms of the equation.The OMR is more strongly supressed by the addition of impurities than tan^2 theta. We conclude that the relaxation ratethat governs Hall effect is not the same as for the magnetoresistance. We also suggest a correspondence between the transport properties and the opening of the pseudogap at a temperature which changes when the La-sr ratio changes, but does not change with the addition of the zinc impurities