1,498 research outputs found
Diffusion and localization of relative strategy scores in the Minority Game
We study the equilibrium distribution of relative strategy scores of agents
in the asymmetric phase () of the basic Minority
Game using sign-payoff, with agents holding two strategies over
histories. We formulate a statistical model that makes use of the gauge freedom
with respect to the ordering of an agent's strategies to quantify the
correlation between the attendance and the distribution of strategies. The
relative score of the two strategies of an agent is described
in terms of a one dimensional random walk with asymmetric jump probabilities,
leading either to a static and asymmetric exponential distribution centered at
for fickle agents or to diffusion with a positive or negative drift for
frozen agents. In terms of scaled coordinates and the
distributions are uniquely given by and in quantitative agreement with
direct simulations of the game. As the model avoids the reformulation in terms
of a constrained minimization problem it can be used for arbitrary payoff
functions with little calculational effort and provides a transparent and
simple formulation of the dynamics of the basic Minority Game in the asymmetric
phase
Modeling a striped pseudogap state
We study the electronic structure within a system of phase-decoupled
one-dimensional superconductors coexisting with stripe spin and charge density
wave order. This system has a nodal Fermi surface (Fermi arc) in the form of a
hole pocket and an antinodal pseudogap. The spectral function in the antinodes
is approximately particle-hole symmetric contrary to the gapped regions just
outside the pocket. We find that states at the Fermi energy are extended
whereas states near the pseudogap energy have localization lengths as short as
the inter-stripe spacing. We consider pairing which has either local d-wave or
s-wave symmetry and find similar results in both cases, consistent with the
pseudogap being an effect of local pair correlations. We suggest that this
state is a stripe ordered caricature of the pseudogap phase in underdoped
cuprates with coexisting spin-, charge-, and pair-density wave correlations.
Lastly, we also model a superconducting state which 1) evolves smoothly from
the pseudogap state, 2) has a signature subgap peak in the density of states,
and 3) has the coherent pair density concentrated to the nodal region.Comment: 12 pages, 12 figures, extended discussion, added references; v3,
added figure of antinodal spectra for normal/pseudo/sc state
Band structure of Charge Ordered Doped Antiferromagnets
We study the distribution of electronic spectral weight in a doped
antiferromagnet with various types of charge order and compare to angle
resolved photoemission experiments on lightly doped LaSrCuO
(LSCO) and electron doped NdCeCuO. Calculations on
in-phase stripe and bubble phases for the electron doped system are both in
good agreement with experiment including in particular the existence of in-gap
spectral weight. In addition we find that for in-phase stripes, in contrast to
anti-phase stripes, the chemical potential is likely to move with doping. For
the hole doped system we find that ``staircase'' stripes which are globally
diagonal but locally vertical or horizontal can reproduce the photoemission
data whereas pure diagonal stripes cannot. We also calculate the magnetic
structure factors of such staircase stripes and find that as the stripe
separation is decreased with increased doping these evolve from diagonal to
vertical separated by a coexistence region. The results suggest that the
transition from horizontal to diagonal stripes seen in neutron scattering on
underdoped LSCO may be a crossover between a regime where the typical length of
straight stripe segments is longer than the inter-stripe spacing to one where
it is shorter and that locally the stripes are always aligned with the Cu-O
bonds.Comment: 13 pages, 16 figure
Addendum to ``Multichannel Kondo screening in a one-dimensional correlated electron system''
This is an addendum to our previous work cond-mat/9705048 (published in
Europhysics Letters 41, 213 (1998)), clarifying the construction of the
two-particle scattering matrices used for studying the magnetic impurity
behavior in a multichannel correlated host.Comment: Addendum to cond-mat/9705048 (Europhys. Lett. 41, 213 (1998)
Nodal-antinodal dichotomy and magic doping fractions in a stripe ordered antiferromagnet
We study a model of a stripe ordered doped antiferromagnet consisting of
coupled Hubbard ladders which can be tuned from quasi-one-dimensional to
two-dimensional. We solve for the magnetization and charge density on the
ladders by Hartree-Fock theory and find a set of solutions with lightly doped
``spin-stripes'' which are antiferromagnetic and more heavily doped anti-phase
``charge-stripes''. Both the spin- and charge-stripes have electronic spectral
weight near the Fermi energy but in different regions of the Brillouin zone;
the spin-stripes in the ``nodal'' region, near (\pi/2,\pi/2), and the
charge-stripes in the ``antinodal'' region, near (\pi,0). We find a striking
dichotomy between nodal and antinodal states in which the nodal states are
essentially delocalized and two-dimensional whereas the antinodal states are
quasi-one-dimensional, localized on individual charge-stripes. For
bond-centered stripes we also find an even-odd effect of the charge periodicity
which could explain the non-monotonous variations with doping of the
low-temperature resistivity in LSCOComment: 6 pages, 6 figures, Expanded and improved, with additional reference
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