365 research outputs found
From local to nonlocal Fermi liquid in doped antiferromagnets
The variation of single-particle spectral functions with doping is studied
numerically within the t-J model. It is shown that corresponding self energies
change from local ones at the intermediate doping to strongly nonlocal ones for
a weakly doped antiferromagnet. The nonlocality shows up most clearly in the
pseudogap emerging in the density of states, due to the onset of short-range
antiferromagnetic correlations.Comment: 4 pages, 3 Postscript figures, revtex, submitted to Phys.Rev.Let
Theory of Underdoped Cuprates
We develop a slave-boson theory for the t-J model at finite doping which
respects an SU(2) symmetry -- a symmetry previously known to be important at
half filling. The mean field phase diagram is found to be consistent with the
phases observed in the cuprate superconductors, which contains d-wave
superconductor, spin gap, strange metal, and Fermi liquid phases. The spin gap
phase is best understood as the staggered flux phase, which is nevertheless
translationally invariant for physical quantities. The electron spectral
function shows small Fermi pockets at low doping which continuously evolve into
the large Fermi surface at high doping concentrations.Comment: 4 pages, latex(revtex,epsf), 3 figure
On single and double soft behaviors in NLSM
In this paper, we study the single and double soft behaviors of tree level
off-shell currents and on-shell amplitudes in nonlinear sigma model(NLSM). We
first propose and prove the leading soft behavior of the tree level currents
with a single soft particle. In the on-shell limit, this single soft emission
becomes the Adler's zero. Then we establish the leading and sub-leading soft
behaviors of tree level currents with two adjacent soft particles. With a
careful analysis of the on-shell limit, we obtain the double soft behaviors of
on-shell amplitudes where the two soft particles are adjacent to each other. By
applying Kleiss-Kuijf (KK) relation, we further obtain the leading and
sub-leading behaviors of amplitudes with two nonadjacent soft particles.Comment: 41 pages, 6 tables, 9 figures, minor revised, more content about
nonadjacent double soft limit, update the reference
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
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
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
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