432 research outputs found
Models of the Pseudogap State of Two-Dimensional Systems
We analyze a number of ``nearly exactly'' solvable models of electronic
spectrum of two-dimensional systems with well-developed fluctuations of short
range order of ``dielectric'' (e.g. antiferromagnetic) or ``superconducting''
type, which lead to the formation of anisotropic pseudogap state on certain
parts of the Fermi surface. We formulate a recurrence procedure to calculate
one-electron Green's function which takes into account all Feynman diagrams in
perturbation series and is based upon the approximate Ansatz for higher-order
terms in this series. Detailed results for spectral densities and density of
states are presented. We also discuss some important points concerning the
justification of our Ansatz for higher-order contributions.Comment: 22 pages, 15 figures, RevTeX 3.0, Postscript figures attache
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
Non - Fermi Liquid Behavior in Fluctuating Gap Model: From Pole to Zero of the Green's function
We analyze non - Fermi liquid (NFL) behavior of fluctuating gap model (FGM)
of pseudogap behavior in both 1D and 2D. We discuss in detail quasiparticle
renormalization (Z - factor), demonstrating a kind of "marginal" Fermi liquid
or Luttinger liquid behavior and topological stability of the "bare" Fermi
surface (Luttinger theorem). In 2D case we discuss effective picture of Fermi
surface "destruction" both in "hot spots" model of dielectric (AFM, CDW)
pseudogap fluctuations, as well as for qualitatively different case of
superconducting d - wave fluctuations, reflecting NFL spectral density behavior
and similar to that observed in ARPES experiments on copper oxides.Comment: 11 pages, 8 figure
Optical conductivity of a quasi-one-dimensional system with fluctuating order
We describe a formally exact method to calculate the optical conductivity of
a one-dimensional system with fluctuating order. For classical phase
fluctuations we explicitly determine the optical conductivity by solving two
coupled Fokker-Planck equations numerically. Our results differ considerably
from perturbation theory and in contrast to Gaussian order parameter
fluctuations show a strong dependence on the correlation length.Comment: 7 pages, 2 figure
Superconductivity in a Toy Model of the Pseudogap State
We analyze superconducting state (both s and d - wave) in a simple exactly
solvable model of pseudogap state, induced by short - range order fluctuations
(e.g. antiferromagnetic), which is based upon model Fermi - surface with "hot
patches". It is shown that superconducting energy gap averaged over these
fluctuations is non zero even for the temperatures larger than mean - field T_c
of superconducting transition in a sample as a whole. For temperatures T>T_c
superconductivity apparently exists within separate regions ("drops"). We study
the spectral density and the density of states and demonstrate that
superconductivity signals itself in these already for T>T_c, while at T_c
itself nothing special happens from this point of view. These anomalies are in
qualitative agreement with a number experiments on underdoped cuprates.Comment: 12 pages, 6 figures, RevTeX 3.0, Postscript figures attache
Superconductivity in an Exactly Solvable Model of the Pseudogap State: Absence of Self Averaging
We analyze the anomalies of superconducting state within a simple exactly
solvable model of the pseudogap state, induced by fluctuations of
``dielectric'' short range order, for the model of the Fermi surface with
``hot'' patches. The analysis is performed for the arbitrary values of the
correlation length xi_{corr} of this short range order. It is shown that
superconducting energy gap averaged over these fluctuations is non zero in a
wide temperature range above T_c - the temperature of homogeneous
superconducting transition. This follows from the absence of self averaging of
the gap over the random field of fluctuations. For temperatures T>T_c
superconductivity apparently appears in separate regions of space (``drops'').
These effects become weaker for shorter correlation lengths xi_{corr} and the
region of ``drops'' on the phase diagram becomes narrower and disappears for
xi_{corr}-->0, however, for the finite values of xi_{corr} the complete self
averaging is absent.Comment: 20 pages, 6 figures, RevTeX 3.0, submitted to JETP, minor misprints
correcte
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
- …