1,828 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]
Hole photoproduction in insulating copper oxide
Basing on t-J model we calculate the k-dependence of a single hole
photoproduction probability for CuO2 plane at zero doping. We also discuss the
radiation of spin-waves which can substantially deform the shape of
photoemission spectra.Comment: latex 8 pages, 3 figure
Anomalous low doping phase of the Hubbard model
We present results of a systematic Quantum-Monte-Carlo study for the
single-band Hubbard model. Thereby we evaluated single-particle spectra (PES &
IPES), two-particle spectra (spin & density correlation functions), and the
dynamical correlation function of suitably defined diagnostic operators, all as
a function of temperature and hole doping. The results allow to identify
different physical regimes. Near half-filling we find an anomalous `Hubbard-I
phase', where the band structure is, up to some minor modifications, consistent
with the Hubbard-I predictions. At lower temperatures, where the spin response
becomes sharp, additional dispersionless `bands' emerge due to the dressing of
electrons/holes with spin excitatons. We present a simple phenomenological fit
which reproduces the band structure of the insulator quantitatively. The Fermi
surface volume in the low doping phase, as derived from the single-particle
spectral function, is not consistent with the Luttinger theorem, but
qualitatively in agreement with the predictions of the Hubbard-I approximation.
The anomalous phase extends up to a hole concentration of 15%, i.e. the
underdoped region in the phase diagram of high-T_c superconductors. We also
investigate the nature of the magnetic ordering transition in the single
particle spectra. We show that the transition to an SDW-like band structure is
not accomplished by the formation of any resolvable `precursor bands', but
rather by a (spectroscopically invisible) band of spin 3/2 quasiparticles. We
discuss implications for the `remnant Fermi surface' in insulating cuprate
compounds and the shadow bands in the doped materials.Comment: RevTex-file, 20 PRB pages, 16 figures included partially as gif. A
full ps-version including ps-figures can be found at
http://theorie.physik.uni-wuerzburg.de/~eder/condmat.ps.gz Hardcopies of
figures (or the entire manuscript) can also be obtained by e-mail request to:
[email protected]
Single Hole Green's Functions in Insulating Copper Oxides at Nonzero Temperature
We consider the single hole dynamics in a modified model at finite
temperature. The modified model includes a next nearest () and next-next
nearest () hopping. The model has been considered before in the zero
temperature limit to explain angle resolved photo-emission measurements. We
extend this consideration to the case of finite temperature where long-range
anti-ferromagnetic order is destroyed, using the self-consistent Born
approximation. The Dyson equation which relates the single hole Green's
functions for a fixed pseudo-spin and for fixed spin is derived. The Green's
function with fixed pseudo-spin is infrared stable but the Green's function
with fixed spin is close to an infrared divergency. We demonstrate how to
renormalize this Green's function in order to assure numerical convergence. At
non-zero temperature the quasi-particle peaks are found to shift down in energy
and to be broadened.Comment: 7 pages, RevTex, 5 Postscript figure
Single hole dynamics in dimerized spin liquids
The dynamics of a single hole in quantum antiferromagnets is influenced by
magnetic fluctuations. In the present work we consider two situations. The
first one corresponds to a single hole in the two leg t-J spin ladder. In this
case the wave function renormalization is relatively small and the
quasiparticle residue of the S=1/2 state remains close to unity. However at
large t/J there are higher spin (S=3/2,5/2,..) bound states of the hole with
the magnetic excitations, and therefore there is a crossover from
quasiparticles with S=1/2 to quasiparticles with higher spin.
The second situation corresponds to a single hole in two coupled
antiferromagnetic planes very close to the point of antiferromagnetic
instability. In this case the hole wave function renormalization is very strong
and the quasiparticle residue vanishes at the point of instability.Comment: 12 pages, 3 figure
Dynamics of spin ladders
We derive an approximate theory for Heisenberg spin ladders with two legs by
mapping the spin dynamics onto the problem of hard-core `bond-Bosons'. The
parameters of the Bosonic Hamiltonian are obtained by matching anomalous
Green's functions to Lanczos results and we find evidence for a strong
renormalization due to quantum fluctuations. Various dynamical spin correlation
functions are calculated and found to be in good agreement with Lanczos
results. We then enlarge the effective Hamiltonian to describe the coupling of
the bond-Bosons to a single hole injected into the system and treat the
hole-dynamics within the `rainbow-diagram' approximation by Schmidt-Rink et.
al. Theoretical predictions for the single hole spectral function are obtained
and found to be in good agreement with Lanczos results.Comment: RevTex-file, 10 PRB pages with 7 eps files. Hardcopies of figures (or
the entire manuscript) can be obtained by e-mail request to:
[email protected]
Knowledge Documentation Based on Automatic Identification and Clustering of Change Intentions in CAD Data of Wiring Harnesses
High amount of changes and increasing complexity in CAD design of wiring harnesses result in a lack of time for documentation and transfer of acquired knowledge. To be able to transfer the gained knowledge efficiently during development automating the identification, analyzation and documentation of changes is necessary. This paper shows a methodology to address this challenge for CAD data of wiring harnesses. Thus, it is shown how interrelated change elements can be combined or separated from each other according to their change intention
Bogoliubov Quasiparticle Excitations in the Two-Dimensional t-J Model
Using a proposed numerical technique for calculating anomalous Green's
functions characteristic of superconductivity, we show that the low-lying
excitations in a wide parameter and doping region of the two-dimensional
model are well described by the picture of dressed Bogoliubov
quasiparticles in the BCS pairing theory. The pairing occurs predominantly in
-wave channel and the energy gap has a size
between quarter and half fillings. Opening of
the superconducting gap in the photoemission and inverse-photoemission spectrum
is demonstrated.Comment: 6 pages, RevTe
Hole-Hole Contact Interaction in the t-J Model
Using an analytical variational approach we calculate the hole-hole contact
interaction on the N\'{e}el background. Solution of the Bethe-Salpeter equation
with this interaction gives bound states in - and p-waves with binding
energies close to those obtained by numerical methods. At the
bound state disappears. In conclusion we discuss the relation between short
range and long range interactions and analogy with the problem of pion
condensation in nuclear matter.Comment: 11 pp. (LATEX), 7 figures (PostScript) appended, report N
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