4,310 research outputs found
Inverse photoemission in strongly correlated electron systems
Based on exact results for small clusters of 2D t-J model we demonstrate the
existence of several distinct `channels' in its inverse photoemission (IPES)
spectrum. Hole-like quasiparticles can either be annihilated completely, or
leave behind a variable number of spin excitations, which formed the `dressing
cloud' of the annihilated hole. In the physical parameter regime the latter
processes carry the bulk of IPES weight and although the Fermi surface takes
the form of hole pockets, the distribution of spectal weight including these
`magnon-bands' in the IPES spectrum is reminiscent of free electrons. The
emerging scenario for Fermiology and spectral weight distribution is shown to
be consistent with photoemission, inverse photemission and de Haas--van Alphen
experiments on cuprate superconductors.Comment: Revtex file, 4 PRB pages + three figures appended as uu-encoded
postscript. Hardcopies of figures (or the entire manuscript) can also be
obtained by e-mail request to: [email protected]
Anomalous Spin and Charge Dynamics of the 2D t-J Model at low doping
We present an exact diagonalization study of the dynamical spin and density
correlation function of the 2D t-J model for hole doping < 25%. Both
correlation functions show a remarkably regular, but completely different
scaling behaviour with both hole concentration and parameter values: the
density correlation function is consistent with that of bosons corresponding to
the doped holes and condensed into the lowest state of the noninteracting band
of width 8t, the spin correlation function is consistent with Fermions in a
band of width J. We show that the spin bag picture gives a natural explanation
for this unusual behaviour.Comment: Revtex-file, 4 PRB pages + 5 figures attached as uu-encoded ps-files
Hardcopies of figures (or the entire manuscript) can also be obtained by
e-mailing to: [email protected]
Space shuttle: Static aerodynamic and control investigation of an expendable second stage with payload alone and with delta wing booster (B-15B-1)
Aerodynamic force and moment coefficients for scale model of expendable second stage modified S-2 alone and mounted piggyback on space shuttle booster from Mach 0.6 to 4.9
Self-energy and Fermi surface of the 2-dimensional Hubbard model
We present an exact diagonalization study of the self-energy of the
two-dimensional Hubbard model. To increase the range of available cluster sizes
we use a corrected t-J model to compute approximate Greens functions for the
Hubbard model. This allows to obtain spectra for clusters with 18 and 20 sites.
The self-energy has several `bands' of poles with strong dispersion and
extended incoherent continua with k-dependent intensity. We fit the self-energy
by a minimal model and use this to extrapolate the cluster results to the
infinite lattice. The resulting Fermi surface shows a transition from hole
pockets in the underdoped regime to a large Fermi surface in the overdoped
regime. We demonstrate that hole pockets can be completely consistent with the
Luttinger theorem. Introduction of next-nearest neighbor hopping changes the
self-energy stronlgy and the spectral function with nonvanishing
next-nearest-neighbor hopping in the underdoped region is in good agreement
with angle resolved photoelectron spectroscopy.Comment: 17 pages, 18 figure
Landau mapping and Fermi liquid parameters of the 2D t-J model
We study the momentum distribution function n(k) in the 2D t-J model on small
clusters by exact diagonalization. We show that n(k) can be decomposed
systematically into two components with Bosonic and Fermionic doping
dependence. The Bosonic component originates from the incoherent motion of
holes and has no significance for the low energy physics. For the Fermionic
component we exlicitely perform the one-to-one Landau mapping between the low
lying eigenstates of the t-J model clusters and those of an equivalent system
of spin-1/2 quasiparticles. This mapping allows to extract the quasiparticle
dispersion, statistics, and Landau parameters. The results show conclusively
that the 2D t-J model for small doping is a Fermi liquid with a `small' Fermi
surface and a moderately strong attractive interaction between the
quasiparticles.Comment: Revtex file, 5 pages with 5 embedded eps-files, hardcopies of figures
(or the entire manuscript) can be obtained by e-mail request to:
[email protected]
Space shuttle: Static stability and control investigation of NR/GD delta wing booster (B-20) and delta wing orbiter (134D), volume 1
Experimental aerodynamic investigations have been made on a .0035 scale model North American Rockwell/General Dynamics version of the space shuttle. Static stability and control data were obtained on the delta wing booster alone (B-20) and with the delta wing orbiter (134D) mounted in various positions on the booster. Six component aerodynamic force and moment data were recorded over an angle of attack range from -10 deg to 24 deg at 0 deg and 6 deg sideslip angles and from -10 deg to +10 deg sideslip at 0 deg angle of attack. Mach number ranged from 0.6 to 4.96
Dynamics of an SO(5) symmetric ladder model
We discuss properties of an exactly SO(5) symmetric ladder model. In the
strong coupling limit we demonstrate how the SO(3)-symmetric description of
spin ladders in terms of bond Bosons can be upgraded to an SO(5)-symmetric
bond-Boson model, which provides a particularly simple example for the concept
of SO(5) symmetry. Based on this representation we show that antiferro-
magnetism on one hand and superconductivity on the other hand can be understood
as condensation of either magnetic or charged Bosons into an RVB vacuum. We
identify exact eigenstates of a finite cluster with general multiplets of the
SO(5) group, and present numerical results for the single particle spectra and
spin/charge correlation functions of the SO(5)-symmetric model and identify
`fingerprints' of SO(5) symmetry in these. In particluar we show that SO(5)
symmetry implies a `generalized rigid band behavior' of the photoemission
spectrum, i.e. spectra for the doped case are rigorously identical to spectra
for spin-polarized states at half-filling. We discuss the problem of adiabatic
continuity between the SO(5) symmetric ladder and the actual t-J ladder and
demonstrate the feasibility of a `Landau mapping' between the two models.Comment: Revtex-file, 16 pages with 15 eps-figures. Hardcopies of Figures (or
the entire manuscript) obtainable by e-mail request to
[email protected]
Hubbard model versus t-J model: The one-particle spectrum
The origin of the apparent discrepancies between the one-particle spectra of
the Hubbard and t-J models is revealed: Wavefunction corrections, in addition
to the three-site terms, should supplement the bare t-J. In this way a
quantitative agreement between the two models is obtained, even for the
intermediate- values appropriate for the high-Tc cuprate superconductors.
Numerical results for clusters of up to 20 sites are presented. The momentum
dependence of the observed intensities in the photoemission spectra of
Sr2CuO2Cl2 are well described by this complete strong-coupling approach.Comment: 4 two-column RevTeX pages, including 4 Postscript figures. Uses epsf.
Accepted for publication in Physical Review B, Rapid Communicatio
Spectral density for a hole in an antiferromagnetic stripe phase
Using variational trial wave function based on the string picture we study
the motion of a single mobile hole in the stripe phase of the doped
antiferromagnet. The holes within the stripes are taken to be static, the
undoped antiferromagnetic domains in between the hole stripes are assumed to
have alternating staggered magnetization, as is suggested by neutron scattering
experiments. The system is described by the t-t'-t''-J model with realistic
parameters and we compute the single particle spectral density.Comment: RevTex-file, 9 PRB pages with 15 .eps and .gif files. To appear in
PRB. Hardcopies of figures (or the entire manuscript) can be obtained by
e-mail request to: [email protected]
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