656 research outputs found
Systematic X-ray absorption study of hole doping in BSCCO - phases
X-ray absorption spectroscopy (XAS) on the O 1s threshold was applied to
Bi-based, single crystalline high temperature superconductors (HTc's), whose
hole densities in the CuO2 planes was varied by different methods. XAS gives
the intensity of the so-called pre-peak of the O 1s line due to the unoccupied
part of the Zhang-Rice (ZR) singlet state. The effects of variation of the
number n of CuO2 - planes per unit cell (n = 1,2,3) and the effect of
La-substitution for Sr for the n = 1 and n = 2 phase were studied
systematically. Furthermore the symmetry of the states could be probed by the
polarization of the impinging radiation.Comment: 4 pages, 2 figures, to appear in the proceedings of SCES2001, Ann
Arbor, August 6-10, 200
Comparative study of the electronic structures of the In and Sn/In2O3 (111) interfaces
The electronic structure of the transparent semiconductor In2O3 has been
studied by angle resolved photoemission spectroscopy upon deposition of
metallic indium and also tin on the surface of the semiconductor. By deposition
of metallic indium on In2O3 (111) single crystals, we detected the formation of
a free-electron like band of effective mass (0.38+-0.05) m0. At low coverages,
metallic In shifts the Fermi level of In2O3 to higher energies and a new
electronic state forms at the metal/semiconductor interface. This state of
two-dimensional character (2D-electron gas) is completely responsible for the
electrical conduction in In2O3 (111) at the surface region and has a band
dispersion, which does not correspond to the previously found surface
accumulation layers in this material. Despite the similarity of the electronic
properties of In and Sn, a larger downward banding was observed by Sn coverage,
which was not accompanied by the appearance of the surface state.Comment: 5 pages, 3 figure
Quasiparticles and Energy Scaling in BiSrCaCuO (=1-3): Angle-Resolved Photoemission Spectroscopy
Angle-resolved photoemission spectroscopy (ARPES) has been performed on the
single- to triple-layered Bi-family high-{\it T} superconductors
(BiSrCaCuO, =1-3). We found a sharp
quasiparticle peak as well as a pseudogap at the Fermi level in the
triple-layered compound. Comparison among three compounds has revealed a
universal rule that the characteristic energies of superconducting and
pseudogap behaviors are scaled with the maximum {\it T}.Comment: 4 pages, 4 figure
Formal Framework for Property-driven Obfuscations
We study the existence and the characterization of function transformers that minimally or maximally modify a function in order to reveal or conceal a certain property. Based on this general formal framework we develop a strategy for the design of the maximal obfuscating transformation that conceals a given property while revealing the desired observational behaviou
Novel Fine-Structure in the Low-Energy Excitation Spectrum of a High-Tc Superconductor by Polarization Dependent Photoemission
Angle-resolved photoemission spectroscopy is performed on single crystals of
the single-layer high-Tc superconductor Bi(2)Sr(2-x)La(x)CuO(6+d) at optimal
doping (x=0.4) in order to study in great detail the Zhang-Rice (ZR) singlet
band at the Fermi level. Besides the high crystal quality the advantages of a
single-layer material are the absence of bilayer effects and the distinct
reduction of thermal broadening. Due to the high energy and angle resolution
and, most important, due to the controlled variation of the polarization vector
of the synchrotron radiation the emission from the ZR singlet band reveals a
distinct fine-structure. It consists of two maxima, the first showing only weak
and the second at EF extremely strong polarization dependence. However, our
observation has enormous consequences for line shape analyses and the
determination of pseudo gaps by photoemission.Comment: 10 pages, 2 figures. to appear in PRB (Rapid Comm.
Strong spin triplet contribution of the first removal state in the insulating regime of Bi2Sr2Ca1-xYxCu2O8+delta
The experimental dispersion of the first removal state in the insulating
regime of Bi2Sr2Ca1-xYxCu2O8+delta is found to differ significantly from that
of other parent materials: oxyclorides and La2CuO4 . For Y-contents of 0.92 > x
> 0.55 due to nonstoichiometric effects in the Bi-O layers, the hole
concentration in the CuO2 -layers is almost constant and on the contrary the
crystal lattice parameters a,b,c change very strongly. This (a,b) parameter
increase and c parameter decrease results in an unconventional three peak
structure at (0,0);(pi/2, pi/2);(pi,pi) for x=0.92. We can describe the
experimental data only beyond the framework of the 3-band pd-model involving
the representations of a new triplet counterpart for the Zhang-Rice singlet
state.Comment: 16 pages, 4 figure
Spectroscopic signatures of spin-charge separation in the quasi-one-dimensional organic conductor TTF-TCNQ
The electronic structure of the quasi-one-dimensional organic conductor
TTF-TCNQ is studied by angle-resolved photoelectron spectroscopy (ARPES). The
experimental spectra reveal significant discrepancies to band theory. We
demonstrate that the measured dispersions can be consistently mapped onto the
one-dimensional Hubbard model at finite doping. This interpretation is further
supported by a remarkable transfer of spectral weight as function of
temperature. The ARPES data thus show spectroscopic signatures of spin-charge
separation on an energy scale of the conduction band width.Comment: 4 pages, 4 figures; to appear in PR
Lifetime of d-holes at Cu surfaces: Theory and experiment
We have investigated the hole dynamics at copper surfaces by high-resolution
angle-resolved photoemission experiments and many-body quasiparticle GW
calculations. Large deviations from a free-electron-like picture are observed
both in the magnitude and the energy dependence of the lifetimes, with a clear
indication that holes exhibit longer lifetimes than electrons with the same
excitation energy. Our calculations show that the small overlap of d- and
sp-states below the Fermi level is responsible for the observed enhancement.
Although there is qualitative good agreement of our theoretical predictions and
the measured lifetimes, there still exist some discrepancies pointing to the
need of a better description of the actual band structure of the solid.Comment: 15 pages, 7 figures, 1 table, to appear in Phys. Rev.
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