18,508 research outputs found
Inversion phenomenon and phase diagram of the distorted diamond chain with the interaction anisotropy
We discuss the anisotropies of the Hamiltonian and the wave-function in an
distorted diamond chain. The ground-state phase diagram of this model
is investigated using the degenerate perturbation theory up to the first order
and the level spectroscopy analysis of the numerical diagonalization data. In
some regions of the obtained phase diagram, the anisotropy of the Hamiltonian
and that of the wave-function are inverted, which we call inversion phenomenon;
the N\'{e}el phase appears for the XY-like anisotropy and the spin-fluid phase
appears for the Ising-like anisotropy. Three key words are important for this
nature, which are frustration, the trimer nature, and the anisotropy.Comment: 4pages, 10 figures, for proceedings of SPQS 200
Microscopic Inhomogeneity and Superconducting Properties of a Two-dimensional Hubbard Model for High- Cuprate
Recent scanning tunneling microscopy measurements on cuprate superconductors
have revealed remarkable spatial inhomogeneities in the single-particle energy
gap. Using cellular dynamical mean-field theory, we study the zero temperature
superconducting properties of a single-band Hubbard model with a spatial
modulation of the electron density. We find that the inhomogeneity in the
electronic structure results in a substantial spatial variation in the
superconducting order parameter and single-particle energy gap, reminiscent of
the experimental results. In particular, we find that the order parameter and
gap amplitudes in the hole-rich regions are significantly enhanced over the
corresponding quantities in a uniform system, if the hole-rich regions are
embedded in regions with smaller hole density.Comment: 6 pages, 4 figures, and 2 table
Enhanced Superconductivity in Superlattices of High- Cuprates
The electronic properties of multilayers of strongly correlated models for
cuprate superconductors are investigated using cluster dynamical mean-field
techniques. We focus on combinations of underdoped and overdoped layers and
find that the superconducting order parameter in the overdoped layers is
enhanced by the proximity effect of the strong pairing scale originating from
the underdoped layers. The enhanced order parameter can even exceed the maximum
value in uniform systems. This behavior is well reproduced in slave-boson
mean-field calculations which also find higher transition temperatures than in
the uniform system.Comment: 4 pages, 4 figure
Metal-Insulator Transition and Spin Degree of Freedom in Silicon 2D Electron Systems
Magnetotransport in 2DES's formed in Si-MOSFET's and Si/SiGe quantum wells at
low temperatures is reported. Metallic temperature dependence of resistivity is
observed for the n-Si/SiGe sample even in a parallel magnetic field of 9T,
where the spins of electrons are expected to be polarized completely.
Correlation between the spin polarization and minima in the diagonal
resistivity observed by rotating the samples for various total strength of the
magnetic field is also investigated.Comment: 3 pages, RevTeX, 4 eps-figures, conference paper (EP2DS-13
Painleve equations from Darboux chains - Part 1: P3-P5
We show that the Painleve equations P3-P5 can be derived (in a unified way)
from a periodic sequence of Darboux transformations for a Schrodinger problem
with quadratic eigenvalue dependency. The general problem naturally divides
into three different branches, each described by an infinite chain of
equations. The Painleve equations are obtained by closing the chain
periodically at the lowest nontrivial level(s). The chains provide ``symmetric
forms'' for the Painleve equations, from which Hirota bilinear forms and Lax
pairs are derived. In this paper (Part 1) we analyze in detail the cases P3-P5,
while P6 will be studied in Part 2.Comment: 23 pages, 1 reference added + minor change
Irregular conformal blocks, with an application to the fifth and fourth Painlev\'e equations
We develop the theory of irregular conformal blocks of the Virasoro algebra.
In previous studies, expansions of irregular conformal blocks at regular
singular points were obtained as degeneration limits of regular conformal
blocks; however, such expansions at irregular singular points were not clearly
understood. This is because precise definitions of irregular vertex operators
had not been provided previously. In this paper, we present precise definitions
of irregular vertex operators of two types and we prove that one of our vertex
operators exists uniquely. Then, we define irregular conformal blocks with at
most two irregular singular points as expectation values of given irregular
vertex operators. Our definitions provide an understanding of expansions of
irregular conformal blocks and enable us to obtain expansions at irregular
singular points.
As an application, we propose conjectural formulas of series expansions of
the tau functions of the fifth and fourth Painlev\'e equations, using
expansions of irregular conformal blocks at an irregular singular point.Comment: 26 page
Spontaneous fourfold-symmetry breaking driven by electron-lattice coupling and strong correlations in high- cuprates
Using dynamical-mean-field theory for clusters, we study the two-dimensional
Hubbard model in which electrons are coupled with the orthorhombic lattice
distortions through the modulation in the hopping matrix. Instability towards
spontaneous symmetry breaking from a tetragonal symmetric phase to an
orthorhombic distorted phase is examined as a function of doping and
interaction strength. A very strong instability is found in the underdoped
pseudogap regime when the interaction strength is large enough to yield the
Mott insulating phase at half filling. The symmetry breaking accompanies the
recovery of quasiparticle weights along one of the two antinodal directions,
leading to the characteristic Fermi arc reconnection. We discuss the
implications of our results to the fourfold symmetry breaking reported in
systems where the underlying crystal does not have any structural anisotropy.Comment: 6 pages with 4 figure
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