181 research outputs found
Circular dichroism and bilayer splitting in the normal state of underdoped (Pb,Bi)Sr(CaY)CuO and overdoped (Pb,Bi)SrCaCuO
We report an ARPES investigation of the circular dichroism in the first
Brillouin zone (BZ) of under- and overdoped Pb-Bi2212 samples. We show that the
dichroism has opposite signs for bonding and antibonding components of the
bilayer-split CuO-band and is antisymmetric with respect to reflections in both
mirror planes parallel to the c-axis. Using this property of the energy and
momentum intensity distributions we prove the existence of the bilayer
splitting in the normal state of the underdoped compound and compare its value
with the splitting in overdoped sample. In agreement with previous studies the
magnitude of the interlayer coupling does not depend significantly on doping.
We also discuss possible origins of the observed dichroism.Comment: 4 RevTex pages, 4 EPS 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
Sustainable Urban Transformation and the Green Urban Economy
This chapter explores the connections between the concepts of sustainable urban transformation and the green urban economy, proposes a framework for understanding how these concepts “fit” together, and makes some practical suggestions for local governments (and national and international policy)
Proof for trivalent Sc ions in Sc2@C84 from high-energy spectroscopy
The electronic structure and the valency of the Sc ions in the endohedral dimetallofullerene Sc 2 @C 84 with
D 2d symmetry are probed using high-energy spectroscopy. Comparison of the Sc 2p ! 3d x-ray-absorption
spectrum with calculated ionic multiplet spectra shows that the Sc ions are trivalent. Detailed multiplet calcu-lations
including covalency indicate that the effective valency of the Sc~III! ions can be described by a formal
charge transfer to the fullerene cage of 2.660.1. This illustrates that a purely ionic picture is not valid for the
electronic structure of Sc 2 @C 84 , and that a more complex picture including finite hybridization between the Sc
and the fullerene cage has to be applied
The normal state Fermi surface of pristine and Pb-doped Bi2212 from ARPES measurements and its photon energy independence
We address the question as to whether the topology of the normal state Fermi
surface of Bi2212 - as seen in angle resolved photoemission - depends on the
photon energy used to measure it. High resolution photoemission spectra and
Fermi surface maps from pristine and Pb-doped Bi2212 are presented, recorded
using both polarised and unpolarised radiation of differing energies. The data
show clearly that no main band crosses the Fermi surface along the GMZ
direction in reciprocal space, even for a photon energy of 32 eV, thus ruling
out the existence of a G-centred, electron-like Fermi surface in this
archetypal high Tc superconductor. The true topology of the normal state Fermi
surface remains that of hole-like barrels centred at the X,Y points of the
Brillouin zone.Comment: 4 pages (revtex), 4 figures (jpg
Superconducting gap in the presence of bilayer splitting in underdoped Bi(Pb)2212
The clearly resolved bilayer splitting in ARPES spectra of the underdoped
Pb-Bi2212 compound rises the question of how the bonding and antibonding sheets
of the Fermi surface are gapped in the superconducting state. Here we compare
the superconducting gaps for both split components and show that within the
experimental uncertainties they are identical. By tuning the relative intensity
of the bonding and antibonding bands using different excitation conditions we
determine the precise {\bf k}-dependence of the leading edge gap. Significant
deviations from the simple cos()-cos() gap function for the
studied doping level are detected.Comment: 5 pages, 4 figures (revtex4
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
Angle resolved photoemission spectroscopy of Sr_2CuO_2Cl_2 - a revisit
We have investigated the lowest binding-energy electronic structure of the
model cuprate Sr_2CuO_2Cl_2 using angle resolved photoemission spectroscopy
(ARPES). Our data from about 80 cleavages of Sr_2CuO_2Cl_2 single crystals give
a comprehensive, self-consistent picture of the nature of the first
electron-removal state in this model undoped CuO_2-plane cuprate. Firstly, we
show a strong dependence on the polarization of the excitation light which is
understandable in the context of the matrix element governing the photoemission
process, which gives a state with the symmetry of a Zhang-Rice singlet.
Secondly, the strong, oscillatory dependence of the intensity of the Zhang-Rice
singlet on the exciting photon-energy is shown to be consistent with
interference effects connected with the periodicity of the crystal structure in
the crystallographic c-direction. Thirdly, we measured the dispersion of the
first electron-removal states along G->(pi,pi) and G->(pi,0), the latter being
controversial in the literature, and have shown that the data are best fitted
using an extended t-J-model, and extract the relevant model parameters. An
analysis of the spectral weight of the first ionization states for different
excitation energies within the approach used by Leung et al. (Phys. Rev. B56,
6320 (1997)) results in a strongly photon-energy dependent ratio between the
coherent and incoherent spectral weight. The possible reasons for this
observation and its physical implications are discussed.Comment: 10 pages, 8 figure
The topology of the Fermi surface of Bi2212 from angle resolved photoemission
We present a study of the topology of the normal state Fermi surface (FS) of
the high Tc superconductor Bi2212 using angle-resolved photoemission. We
present FS mapping experiments, recorded using unpolarised radiation with high
(E,k) resolution, and an extremely dense sampling of k-space. In addition,
synchrotron radiation-based ARPES has been used to prove the energy
independence of the FS as seen by photoemission. We resolve the current
controversy regarding the normal state FS in Bi2212. The true picture is
simple, self-consistent and robust: the FS is hole-like, with the form of
rounded tubes centred on the corners of the Brillouin zone. Two further types
of features are also clearly observed: shadow FSs, and diffraction replicas of
the main FS caused by passage of the photoelectrons through the modulated Bi-O
planes.Comment: M2S-HTSC-VI conference paper (4 pages, 3 eps. figures), using
Elsevier style espcrc2.st
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