548 research outputs found
Doping dependence of chemical potential and entropy in hole- and electron-doped high-Tc cuprates
We examine the thermodynamic properties of the hole- and electron-doped
cuprates by using the t-t'-t''-J model. We find that the chemical potential
shows different doping dependence between the hole and electron dopings. Recent
experimental data of the chemical potential shift are reproduced except for
lightly underdoped region in the hole doping where stripe and/or charge
inhomogeneity are expected to be important. The entropy is also calculated as a
function of the carrier concentration. It is found that the entropy of the
electron-doped system is smaller than that of the hole-doped systems. This is
related to strong antiferromagnetic short-range correlation that survives in
the electron-doped system.Comment: REVTeX4, 3 pages, 3 figures, to appear in Phys. Rev.
Anomalous temperature dependence of the single-particle spectrum in the organic conductor TTF-TCNQ
The angle-resolved photoemission spectrum of the organic conductor TTF-TCNQ
exhibits an unusual transfer of spectral weight over a wide energy range for
temperatures 60K<T<260K. In order to investigate the origin of this finding,
here we report numerical results on the single-particle spectral weight
A(k,omega) for the one-dimensional (1D) Hubbard model and, in addition, for the
1D extended Hubbard and the 1D Hubbard-Holstein models. Comparisons with the
photoemission data suggest that the 1D Hubbard model is not sufficient for
explaining the unusual T dependence, and the long-range part of the Coulomb
repulsion also needs to be included.Comment: 4 pages, 4 figure
Temperature dependence of spinon and holon excitations in one-dimensional Mott insulators
Motivated by the recent angle-resolved photoemission spectroscopy (ARPES)
measurements on one-dimensional Mott insulators, SrCuO and
NaVO, we examine the single-particle spectral weight
of the one-dimensional (1D) Hubbard model at half-filling. We are particularly
interested in the temperature dependence of the spinon and holon excitations.
For this reason, we have performed the dynamical density matrix renormalization
group and determinantal quantum Monte Carlo (QMC) calculations for the
single-particle spectral weight of the 1D Hubbard model. In the QMC data, the
spinon and holon branches become observable at temperatures where the
short-range antiferromagnetic correlations develop. At these temperatures, the
spinon branch grows rapidly. In the light of the numerical results, we discuss
the spinon and holon branches observed by the ARPES experiments on
SrCuO. These numerical results are also in agreement with the
temperature dependence of the ARPES results on NaVO.Comment: 8 pages, 8 figure
Drude Weight of the Two-Dimensional Hubbard Model -- Reexamination of Finite-Size Effect in Exact Diagonalization Study --
The Drude weight of the Hubbard model on the two-dimensional square lattice
is studied by the exact diagonalizations applied to clusters up to 20 sites. We
carefully examine finite-size effects by consideration of the appropriate
shapes of clusters and the appropriate boundary condition beyond the imitation
of employing only the simple periodic boundary condition. We successfully
capture the behavior of the Drude weight that is proportional to the squared
hole doping concentration. Our present result gives a consistent understanding
of the transition between the Mott insulator and doped metals. We also find, in
the frequency dependence of the optical conductivity, that the mid-gap
incoherent part emerges more quickly than the coherent part and rather
insensitive to the doping concentration in accordance with the scaling of the
Drude weight.Comment: 9 pages with 10 figures and 1 table. accepted in J. Phys. Soc. Jp
Electronic States in the Antiferromagnetic Phase of Electron-Doped High-Tc Cuprates
We investigate the electronic states in the antiferromagnetic (AF) phase of
electron-doped cuprates by using numerically exact diagonalization technique
for a t-t'-t''-J model. When AF correlation develops with decreasing
temperature, a gaplike behavior emerges in the optical conductivity.
Simultaneously, the coherent motion of carriers due to the same sublattice
hoppings is enhanced. We propose that the phase is characterized as an AF state
with small Fermi surface around the momentum k=(\pi,0) and (0,\pi). This is a
remarkable contrast to the behavior of hole-doped cuprates.Comment: RevTeX, 5 pages, 4 figures, to appear in Phys. Rev. B Brief Report
Angle-resolved photoemission in high Tc cuprates from theoretical viewpoints
The angle-resolved photoemission (ARPES) technique has been developed rapidly
over the last decay, accompanied by the improvement of energy and momentum
resolutions. This technique has been established as the most powerful tool to
investigate the high Tc cuprate superconductors. We review recent ARPES data on
the cuprates from a theoretical point of view, with emphasis on the systematic
evolution of the spectral weight near the momentum (pi,0) from insulator to
overdoped systems. The effects of charge stripes on the ARPES spectra are also
reviewed. Some recent experimental and theoretical efforts to understand the
superconducting state and the pseudogap phenomenon are discussed.Comment: Review, 25 pages, with 22 GIF figures. To appear in Supercond. Sci.
Technol. Vol. 13 April 2000. A version including PS figures can be found at
http://www.maekawa-lab.imr.tohoku.ac.jp/TOHYAMA/tohyama.ps.g
Momentum Dependence of Resonant Inelastic X-Ray Scattering Spectrum in Insulating Cuprates
The resonant inelastic x-ray scattering spectrum in insulating cuprates is
examined by using the exact diagonalization technique on small clusters in the
two-dimensional Hubbard model with second and third neighbor hopping terms.
When the incident photon energy is tuned near the Cu K absorption edges, we
find that the features of the unoccupied upper Hubbard band can be extracted
from the spectrum through an anisotropic momentum dependence. They provide an
opportunity for the understanding of the different behavior of hole- and
electron-doped superconductors.Comment: 4 pages with 4 figures, to be published in PR
Nonlinear optical response and spin-charge separation in one-dimensional Mott insulators
We theoretically study the nonlinear optical response and photoexcited states
of the Mott insulators. The nonlinear optical susceptibility \chi^(3) is
calculated by using the exact diagonalization technique on small clusters. From
the systematic study of the dependence of \chi^(3) on dimensionality, we find
that the spin-charge separation plays a crucial role in enhancing \chi^(3) in
the one-dimensional (1D) Mott insulators. Based on this result, we propose a
holon-doublon model, which describes the nonlinear response in the 1D Mott
insulators. These findings show that the spin-charge separation will become a
key concept of optoelectronic devices.Comment: 5 pages with 3 figures, to appear in PRB RC, 15 August 200
Quasiparticles and c-axis coherent hopping in high T_c superconductors
We study the problem of the low-energy quasiparticle spectrum of the extended
t-J model and analyze the coherent hopping between weakly coupled planes
described by this model. Starting with a two-band model describing the Cu-O
planes and the unoccupied bands associated to the metallic atoms located in
between the planes, we obtain effective hopping matrix elements describing the
c-axis charge transfer. A computational study of these processes shows an
anomalously large charge anisotropy for doping concentrations around and below
the optimal doping.Comment: 4 pages, 3 figure
Phase diagram of a Bose gas near a wide Feshbach resonance
In this paper, we study the phase diagram of a homogeneous Bose gas with a
repulsive interaction near a wide Feshbach resonance at zero temperature. The
Bose-Einstein-condensation (BEC) state of atoms is a metastable state. When the
scattering length exceeds a critical value depending on the atom density
, , the molecular excitation energy is imaginary and the atomic
BEC state is dynamically unstable against molecule formation. The BEC state of
diatomic molecules has lower energy, where the atomic excitation is gapped and
the molecular excitation is gapless. However when the scattering length is
above another critical value, , the molecular BEC state becomes a
unstable coherent mixture of atoms and molecules. In both BEC states, the
binding energy of diatomic molecules is reduced due to the many-body effect.Comment: 5 pages, 4 figure
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