1,068 research outputs found
Dynamical mean field theory of optical third harmonic generation
We formulate the third harmonic generation (THG) within the dynamical mean
field theory (DMFT) approximation of the Hubbard model. In the limit of large
dimensions, where DMFT becomes exact, the vertex corrections to current
vertices are identically zero, and hence the calculation of the THG spectrum
reduces to a time-ordered convolution, followd by appropriate analytic
continuuation. We present the typical THG spectrum of the Hubbard model
obtained by this method. Within our DMFT calculation, we observe a nontrivial
approximate {\em scaling} function describing the THG spectra in all Mott
insulators, independent of the gap magnitude.Comment: 4 eps figure
Comment on "Origin of Giant Optical Nonlinearity in Charge-Transfer--Mott Insulators: A New Paradigm for Nonlinear Optics"
Comment on Phys. Rev. Lett. 86, 2086 (2001)Comment: 1 page, 1 eps figur
Charge dynamics of Ca_{2-x}Na_{x}CuO_{2}Cl_{2} as a correlated electron system with the ideal tetragonal lattice
We report the reflectivity and the resistivity measurement of
Ca_{2-x}Na_{x}CuO_{2}Cl_{2} (CNCOC), which has a single-CuO2-plane lattice with
no orthorhombic distortion. The doping dependence of the in-plane optical
conductivity spectra for CNCOC is qualitatively the same to those of other
cuprates, but a slight difference between CNCOC and LSCO, i.e., the absence of
the 1.5 eV peak in CNCOC, can be attributed to the smaller charge-stripe
instability in CNCOC. The temperature dependence of the optical onductivity
spectra of CNCOC has been analyzed both by the two-component model
(Drude+Lorentzian) and by the one-component model (extended-Drude analysis).
The latter analysis gives a universal trend of the scattering rate Gamma(omega)
with doping. It was also found that Gamma(omega) shows a saturation behavior at
high frequencies, whose origin is the same as that of resistivity saturation at
high temperatures.Comment: 8 pages, 11 figures, to be published in Phys. Rev.
Nonlinear Optical Response in two-dimensional Mott Insulators
We study the third-order nonlinear optical susceptibility and
photoexcited states of two-dimensional (2D) Mott insulators by using an
effective model in the strong-coupling limit of a half-filled Hubbard model. In
the numerically exact diagonalization calculations on finite-size clusters, we
find that the coupling of charge and spin degrees of freedom plays a crucial
role in the distribution of the dipole-allowed states with odd parity and the
dipole-forbidden states with even parity in the photoexcited states. This is in
contrast with the photoexcited states in one dimension, where the charge and
spin degrees of freedom are decoupled. In the third-harmonic generation (THG)
spectrum, main contribution is found to come from the process of three-photon
resonance associated with the odd-parity states. As a result, the two-photon
resonance process is less pronounced in the THG spectrum. The calculated THG
spectrum is compared with recent experimental data. We also find that
with cross-polarized configuration of pump and probe photons shows
spectral distributions similar to with co-polarized configuration,
although the weight is small. These findings will help the analyses of the
experimental data of in the 2D Mott insulators.Comment: 9 pages,5 figures,RevTeX
Nonlinear Optical Response of Spin Density Wave Insulators
We calculate the third order nonlinear optical response in the Hubbard model
within the spin density wave (SDW) mean field ansatz in which the gap is due to
onsite Coulomb repulsion. We obtain closed-form analytical results in one
dimension (1D) and two dimension (2D), which show that nonlinear optical
response in SDW insulators in 2D is stronger than both 3D and 1D. We also
calculate the two photon absorption (TPA) arising from the stress tensor term.
We show that in the SDW, the contribution from stress tensor term to the
low-energy peak corresponding to two photon absorption becomes identically zero
if we consider the gauge invariant current properly.Comment: we use \psfrag in figur
Microcracks, spall and fracture in glass : A study using short pulsed laser shock waves
Copyright 1998 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics, 83(7), 3583-3594, 1998 and may be found at http://dx.doi.org/10.1063/1.36657
Nonlinear Optical Response Functions of Mott Insulators Based on Dynamical Mean Field Approximation
We investigate the nonlinear optical susceptibilities of Mott insulators with
the dynamical mean field approximation. The two-photon absorption (TPA) and the
third-harmonic generation (THG) spectra are calculated, and the classification
by the types of coupling to external fields shows different behavior from
conventional semiconductors. The direct transition terms are predominant both
in the TPA and THG spectra, and the importance of taking all types of
interaction with the external field into account is illustrated in connection
with the THG spectrum and dcKerr effect. The dependence of the TPA and THG
spectra on the Coulomb interaction indicate a scaling relation. We apply this
relation to the quantitative evaluation and obtain results comparable to those
of experiments.Comment: 14 pages, 12 figure
Study of Liquefaction Damages of Quay-Walls and Breakwaters During Kobe Earthquake
During Kobe Earthquake, very extensive damages of harbor facilities such as quay-wall and breakwater occurred in Kobe Port and also along the coastal areas between Kobe and Osaka cities. Major causes of the damages were the liquefaction of sands underlying and behind the concrete caisson and also strong earthquake shaking force on the caisson. The degree of damage varied considerably depending on location and also on the size of structure. In order to understand the mechanism of damage as well as the factors that controlled the degree of damage, it was necessary to examine and analyze the case records of damages of these structures. This paper describes the result of such study on liquefaction damage of quay-walls and breakwaters. Through the study, it was found that the movement of sand at shallow depth below the caisson base is mainly responsible for a large settlement of caisson, but the mode of deformation is different between quay wall and breakwater. Also an effective stress liquefaction analysis was performed on the damaged quay-walls and breakwaters in order to check the applicability of effective stress liquefaction analysis on damage assessment. It was found that the effective stress analysis may be used to establish the overall trend of damage variation with the intensity of seismic motion, but problems exist in setting the dynamic parameters for the analysis, such as damping parameters, in order to obtain a reliable result
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