5,714 research outputs found
Generalized - Model
By parameterizing the t-j model we present a new electron correlation model
with one free parameter for high-temperature superconductivity. This model is
of symmetry. The energy spectrums are shown to be modulated by
the free parameter in the model. The solution and symmetric structures of the
Hilbert space, as well as the Bethe ansatz approach are discussed for special
cases.Comment: 13 page, Latex, to appear in J. Phys.
Polaron in t-J model
We present numeric results for ground state and angle resolved photoemission
spectra (ARPES) for single hole in t-J model coupled to optical phonons. The
systematic-error free diagrammatic Monte Carlo is employed where the Feynman
graphs for the Matsubara Green function in imaginary time are summed up
completely with respect to phonons variables, while magnetic variables are
subjected to non-crossing approximation. We obtain that at electron-phonon
coupling constants relevant for high Tc cuprates the polaron undergoes
self-trapping crossover to strong coupling limit and theoretical ARPES
demonstrate features observed in experiment: a broad peak in the bottom of the
spectra has momentum dependence which coincides with that of hole in pure t-J
model.Comment: 4 pages, 4 figure
Superconductivity in the t-J model
A comparison of microscopic theories of superconductivity in the limit of
strong electron correlations is presented. We consider results for the
two-dimensional t-J model obtained within the projection technique for the
Green functions in terms of the Hubbard operators and the slave-fermion
representation for the RVB state. It is argued that the latter approach
resulting in the odd-symmetry p-wave pairing for fermions is inadequate.Comment: 11 pages, RevTex, 1 figure, to appear in Condensed Matter Physics
v.5, No.4 (2002)(Lviv, Ukraine) v.2: corrected typo
Stripes and the t-J model
We investigate the two-dimensional t-J model at a hole doping of x = 1/8 and
J/t = 0.35 with exact diagonalization. The low-energy states are uniform (not
striped). We find numerous excited states with charge density wave structures,
which may be interpreted as striped phases. Some of these are consistent with
neutron scattering data on the cuprates and nickelates.Comment: 4 pages; 4 eps figures included in text; Revte
Pi excitation of the t-J model
In this paper, we present analytical and numerical calculations of the pi
resonance in the t-J model. We show in detail how the pi resonance in the
particle-particle channel couples to and appears in the dynamical spin
correlation function in a superconducting state. The contribution of the pi
resonance to the spin excitation spectrum can be estimated from general
model-independent sum rules, and it agrees with our detailed calculations. The
results are in overall agreement with the exact diagonalization studies of the
t-J model. Earlier calculations predicted the correct doping dependence of the
neutron resonance peak in the YBCO superconductor, and in this paper detailed
energy and momentum dependence of the spin correlation function is presented.
The microscopic equations of motion obtained within current formalism agree
with that of the SO(5) nonlinear sigma model, where the pi resonance is
interpreted as a pseudo Goldstone mode of the spontaneous SO(5) symmetry
breaking.Comment: 33 pages, LATEX, 14 eps fig
Spin diffusion of the t-J model
The spin-diffusion constant of the 2D model is calculated for the first
time using an analytical approach at high temperatures and a recently-developed
numerical method based on the Lanczos technique combined with random sampling
in the intermediate temperature regime. A simple relation, ,
between spin conductivity and spin diffusion is established and used to
calculate the latter. In the high-temperature and low-doping limit the
calculated diffusion constant agrees with known results for the Heisenberg
model. At small hole doping, increases approximately linearly with
doping, which leads us to an important conclusion that hopping processes
enhance spin diffusion at high temperatures. At modest hole doping, , diffusion exhibits a nonmonotonic temperature dependence, which
indicates anomalous spin dynamics at small frequencies.Comment: 12 pages with figure
Checkerboard patterns in the t-J model
Using the density matrix renormalization group, we study the possibility of
real space checkerboard patterns arising as the ground states of the t-J model.
We find that checkerboards with a commensurate (pi,pi) background are not low
energy states and can only be stabilized with large external potentials.
However, we find that striped states with charge density waves along the
stripes can form approximate checkerboard patterns. These states can be
stabilized with a very weak external field aligning and pinning the CDWs on
different stripes.Comment: 4 pages, 5 figure
Charge susceptibility in the t-J model
Momentum and doping dependence of the static charge susceptibility \chi(q) in
the t-t'-J model is investigated. Correlations lead to a strongly momentum
dependent renormalization of \chi(q). The charge susceptibility near (\pi,\pi)
region of the Brillouin zone is strongly suppressed as the hole density \delta
is decreased. However, contrary to naive expectations, \chi(q) around q =
(\pi,0) and (0,\pi) remains large and practically unchanged at \delta \sim
0.1-0.5. This effect is consistent with a tendency towards low-energy charge
fluctuations with the wave vectors along the \Gamma-X direction, reported in
earlier studies. Our main finding is that the above trends are amplified by
J-driven pairing effects, indicating that the pseudogap formation may promote
the charge inhomogeneity. The next-nearest hopping t' leads to weakening of the
above momentum-selective renormalizations of \chi(q). We analyze the effects of
long-range Coulomb interaction, taking into account a layered structure of
cuprates. As an application, the results are discussed in the context of
bond-stretching phonon softening in hole-doped cuprates. In particular, a
peculiar doping and momentum dependence of the electron-phonon coupling
constant is found.Comment: 12 pages, 11 figures, references added, explanations provided on the
meaning and limitations of our formalis
Spinon-Holon binding in model
Using a phenomenological model, we discuss the consequences of spinon-holon
binding in the U(1) slave-boson approach to model. Within a small
( hole concentration) expansion, we show that spinon-holon binding produces
a pseudo-gap normal state with a segmented Fermi surface and the
superconducting state is formed by opening an "additional" d-wave gap on the
segmented Fermi surface. The d-wave gap merge with the pseudo-gap smoothly as
temperature . The quasi-particles in the superconducting state are
coupled to external electromagnetic field with a coupling constant of order
where , depending on the strength of the
effective spinon-holon binding potential.Comment: 9 pages, 3 figure
Spin Dynamics for the t-J Model
The spin dynamics at the finite temperature for the t-J model in the
underdoped and optimal doped regimes is studied within the fermion-spin theory.
It is shown that the dynamical spin structure factor spectrum at the
antiferromagnetic wave vector are separated as low- and
high-frequency parts, respectively, but the high-frequency part is suppressed
in the dynamical susceptibility spectrum , while the
low-frequency part is the temperature dependent, which are in qualitative
agreement with the experiments and numerical simulations.Comment: 3 pages, three figures are adde
- …