957 research outputs found
Quasiparticle spectrum in a nearly antiferromagnetic Fermi liquid: shadow and flat bands
We consider a two-dimensional Fermi liquid in the vicinity of a
spin-density-wave transition to a phase with commensurate antiferromagnetic
long-range order. We assume that near the transition, the Fermi surface is
large and crosses the magnetic Brillouin zone boundary. We show that under
these conditions, the self-energy corrections to the dynamical spin
susceptibility, , and to the quasiparticle spectral function
function, , are divergent near the transition. We identify and
sum the series of most singular diagrams, and obtain a solution for and an approximate solution for . We show that (i)
at a given, small has an extra peak at (`shadow
band'), and (ii) the dispersion near the crossing points is much flatter than
for free electrons. The relevance of these results to recent photoemission
experiments in and systems is discussed.Comment: a sign and amplitude of the vertex renormalization and few typos are
correcte
Study of ARPES data and d-wave superconductivity using electronic models in two dimensions
We review the results of an extensive investigation of photoemission spectral
weight using electronic models for the high-Tc superconductors. Here we show
that some recently reported unusual features of the cuprates namely the
presence of (i) flat bands, (ii) small quasiparticle bandwidths, and (iii)
antiferromagnetically induced weight, have all a natural explanation within the
context of holes moving in the presence of robust antiferromagnetic
correlations. Introducing interactions among the hole carriers, a model is
constructed which has superconductivity, an optimal
doping of (caused by the presence of a large density of states at
the top of the valence band), and a critical temperature .Comment: 11 pages Z-compressed postscript, to appear in the Proceedings to the
Stanford Conference on Spectroscopies in Novel superconductor
Substrate specificity of bacterial oligosaccharyltransferase suggests a common transfer mechanism for the bacterial and eukaryotic systems
The PgIB oligosaccharyltransferase (OTase) of Campylobacter jejuni can be functionally expressed in Escherichia coli, and its relaxed oligosaccharide substrate specificity allows the transfer of different glycans from the lipid carrier undecaprenyl pyrophosphate to an acceptor protein. To investigate the substrate specificity of PgIB, we tested the transfer of a set of lipid-linked polysaccharides in E. coli and Salmonella enterica serovar Typhimurium. A hexose linked to the C-6 of the monosaccharide at the reducing end did not inhibit the transfer of the O antigen to the acceptor protein. However, PgIB required an acetamido group at the C-2. A model for the mechanism of PgIB involving this functional group was proposed. Previous experiments have shown that eukaryotic OTases have the same requirement, suggesting that eukaryotic and prokaryotic OTases catalyze the transfer of oligosaccharides by a conserved mechanism. Moreover, we demonstrated the functional transfer of the C. jejuni glycosylation system into S. enterica. The elucidation of the mechanism of action and the substrate specificity of PgIB represents the foundation for engineering glycoproteins that will have an impact on biotechnology
Implications of Charge Ordering for Single-Particle Properties of High-Tc Superconductors
The consequences of disordered charge stripes and antiphase spin domains for
the properties of the high-temperature superconductors are studied. We focus on
angle-resolved photoemission spectroscopy and optical conductivity, and show
that the many unusual features of the experimentally observed spectra can be
understood naturally in this way. This interpretation of the data, when
combined with evidence from neutron scattering and NMR, suggests that
disordered and fluctuating stripe phases are a common feature of
high-temperature superconductors.Comment: 4 pages, figures by fax or mai
Bi-layer splitting in overdoped high cuprates
Recent angle-resolved photoemission data for overdoped Bi2212 are explained.
Of the peak-dip-hump structure, the peak corresponds the component
of a hole condensate which appears at . The fluctuating part of this same
condensate produces the hump. The bilayer splitting is large enough to produce
a bonding hole and an electron antibonding quasiparticle Fermi surface. Smaller
bilayer splittings observed in some experiments reflect the interaction of the
peak structure with quasiparticle states near, but not at, the Fermi surface.Comment: 4 pages with 2 figures - published versio
Electronic excitations in BiSrCaCuO : Fermi surface, dispersion, and absence of bilayer splitting
From a detailed study, including polarization dependence, of the normal state
angle-resolved photoemission spectra for BiSrCaCuO, we find
only one CuO band related feature. All other spectral features can be
ascribed either to umklapps from the superlattice or to ``shadow bands''. Even
though the dispersion of the peaks looks like band theory, the lineshape is
anomalously broad and no evidence is found for bilayer splitting. We argue that
the ``dip feature'' in the spectrum below arises not from bilayer
splitting, but rather from many body effects.Comment: 4 pages, revtex, 3 uuencoded postscript figure
ARPES study of Pb doped Bi_2Sr_2CaCu_2O_8 - a new Fermi surface picture
High resolution angle resolved photoemission data from Pb doped
Bi_2Sr_2CaCu_2O_8 (Bi2212) with suppressed superstructure is presented.
Improved resolution and very high momentum space sampling at various photon
energies reveal the presence of two Fermi surface pieces. One has the hole-like
topology, while the other one has its van Hove singularity very close to
(pi,0), its topology at some photon energies resembles the electron-like piece.
This result provides a unifying picture of the Fermi surface in the Bi2212
compound and reconciles the conflicting reports.Comment: 4 pages, 4 figure
Surprises in the doping dependence of the Fermi surface in Bi(Pb)-2212
A detailed and systematic ARPES investigation of the doping-dependence of the
normal state Fermi surface (FS) of modulation-free (Pb,Bi)-2212 is presented.
The FS does not change in topology away from hole-like at any stage. The data
reveal, in addition, a number of surprises. Firstly the FS area does not follow
the usual curve describing Tc vs x for the hole doped cuprates, but is
down-shifted in doping by ca. 0.05 holes per Cu site, indicating either the
break-down of Luttinger's theorem or the consequences of a significant bi-layer
splitting of the FS. Secondly, the strong k-dependence of the FS width is shown
to be doping independent. Finally, the relative strength of the shadow FS has a
doping dependence mirroring that of Tc.Comment: 5 pages, 4 figures (revtex
Hole Doping Evolution of the Quasiparticle Band in Models of Strongly Correlated Electrons for the High-T_c Cuprates
Quantum Monte Carlo (QMC) and Maximum Entropy (ME) techniques are used to
study the spectral function of the one band Hubbard model
in strong coupling including a next-nearest-neighbor electronic hopping with
amplitude . These values of parameters are chosen to improve the
comparison of the Hubbard model with angle-resolved photoemission (ARPES) data
for . A narrow quasiparticle (q.p.) band is observed in the
QMC analysis at the temperature of the simulation , both at and away
from half-filling. Such a narrow band produces a large accumulation of weight
in the density of states at the top of the valence band. As the electronic
density decreases further away from half-filling, the chemical
potential travels through this energy window with a large number of states, and
by it has crossed it entirely. The region near momentum
and in the spectral function is more sensitive to doping
than momenta along the diagonal from to . The evolution with
hole density of the quasiparticle dispersion contains some of the features
observed in recent ARPES data in the underdoped regime. For sufficiently large
hole densities the ``flat'' bands at cross the Fermi energy, a
prediction that could be tested with ARPES techniques applied to overdoped
cuprates. The population of the q.p. band introduces a {\it hidden} density in
the system which produces interesting consequences when the quasiparticles are
assumed to interact through antiferromagnetic fluctuations and studied with the
BCS gap equation formalism. In particular, a region of extended s-wave is found
to compete with d-wave in the overdoped regime, i.e. when the chemical
potential has almost entirely crossed the q.p.Comment: 14 pages, Revtex, with 13 embedded ps figures, submitted to Phys.
Rev. B., minor modifications in the text and in figures 1b, 2b, 3b, 4b, and
6
and Oxygen Stoichiometry: Structure, Resistivity, Fermi Surface Topology and Normal State Properties
(2212) single crystal samples
were studied using transmission electron microscopy (TEM), plane
() and axis () resistivity, and high resolution
angle-resolved ultraviolet photoemission spectroscopy (ARUPS). TEM reveals that
the modulation in the axis for doped 2212 is dominantly
of type that is not sensitive to the oxygen content of the system, and the
system clearly shows a structure of orthorhombic symmetry. Oxygen annealed
samples exhibit a much lower axis resistivity and a resistivity minimum at
K. He-annealed samples exhibit a much higher axis resistivity and
behavior below 300K. The Fermi surface (FS) of oxygen annealed
2212 mapped out by ARUPS has a pocket in the FS around the
point and exhibits orthorhombic symmetry. There are flat, parallel sections of
the FS, about 60\% of the maximum possible along , and about 30\%
along . The wavevectors connecting the flat sections are about
along , and about along , rather than . The symmetry of the near-Fermi-energy dispersing
states in the normal state changes between oxygen-annealed and He-annealed
samples.Comment: APS_REVTEX 3.0, 49 pages, including 11 figures, available upon
request. Submitted to Phys. Rev. B
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