1,071 research outputs found
SU(2) approach to the pseudogap phase of high-temperature superconductors: electronic spectral functions
We use an SU(2) mean-field theory approach with input from variational
wavefunctions of the t-J model to study the electronic spectra in the pseudogap
phase of cuprates. In our model, the high-temperature state of underdoped
cuprates is realized by classical fluctuations of the order parameter between
the d-wave superconductor and the staggered-flux state. Spectral functions of
the intermediate and the averaged states are computed and analyzed. Our model
predicts a photoemission spectrum with an asymmetric gap structure
interpolating between the superconducting gap centered at the Fermi energy and
the asymmetric staggered-flux gap. This asymmetry of the gap changes sign at
the point where the Fermi surface crosses the diagonal (\pi,0)-(0,\pi).Comment: 7 pages, 10 figures; estimate of applicable temperature range
corrected and refs. added, ref. to ARPES paper added; minor changes to
published versio
Aspects of Duality in Nodal Liquids
Starting from a microscopic t-J like model and a SU(2) spin-charge separation
ansatz, a relativistic continuum gauge lagrangian is obtained in the vicinity
of a nodal point of the Fermi surface. The excitations in the pseudogap phase
are described by topological excitations in the dual model which has a Z_2
global symmetry due to the effect of instantons. Confinement of spinon and
holons emerge from this picture. The adjoint and fundamental strings are
associated with stripes. As the spin gap decreases a local Z_2 symmetry
emerges.Comment: 15 pages revtex, no figure
The coherent {\it d}-wave superconducting gap in underdoped LaSrCuO as studied by angle-resolved photoemission
We present angle-resolved photoemission spectroscopy (ARPES) data on
moderately underdoped LaSrCuO at temperatures below and
above the superconducting transition temperature. Unlike previous studies of
this material, we observe sharp spectral peaks along the entire underlying
Fermi surface in the superconducting state. These peaks trace out an energy gap
that follows a simple {\it d}-wave form, with a maximum superconducting gap of
14 meV. Our results are consistent with a single gap picture for the cuprates.
Furthermore our data on the even more underdoped sample
LaSrCuO also show sharp spectral peaks, even at the
antinode, with a maximum superconducting gap of 26 meV.Comment: Accepted by Phys. Rev. Let
ARPES on HTSC: simplicity vs. complexity
A notable role in understanding of microscopic electronic properties of high
temperature superconductors (HTSC) belongs to angle resolved photoemission
spectroscopy (ARPES). This technique supplies a direct window into reciprocal
space of solids: the momentum-energy space where quasiparticles (the electrons
dressed in clouds of interactions) dwell. Any interaction in the electronic
system, e.g. superconducting pairing, leads to modification of the
quasi-particle spectrum--to redistribution of the spectral weight over the
momentum-energy space probed by ARPES. A continued development of the technique
had an effect that the picture seen through the ARPES window became clearer and
sharper until the complexity of the electronic band structure of the cuprates
had been resolved. Now, in an optimal for superconductivity doping range, the
cuprates much resemble a normal metal with well predicted electronic structure,
though with rather strong electron-electron interaction. This principal
disentanglement of the complex physics from complex structure reduced the
mystery of HTSC to a tangible problem of interaction responsible for
quasi-particle formation. Here we present a short overview of resent ARPES
results, which, we believe, denote a way to resolve the HTSC puzzle.Comment: A review written for a special issue of FN
The change of Fermi surface topology in Bi2Sr2CaCu2O8 with doping
We report the observation of a change in Fermi surface topology of
Bi2Sr2CaCu2O8 with doping. By collecting high statistics ARPES data from
moderately and highly overdoped samples and dividing the data by the Fermi
function, we answer a long standing question about the Fermi surface shape of
Bi2Sr2CaCu2O8 close to the (pi,0) point. For moderately overdoped samples
(Tc=80K) we find that both the bonding and antibonding sheets of the Fermi
surface are hole-like. However for a doping level corresponding to Tc=55K we
find that the antibonding sheet becomes electron-like. This change does not
directly affect the critical temperature and therefore the superconductivity.
However, since similar observations of the change of the topology of the Fermi
surface were observed in LSCO and Bi2Sr2Cu2O6, it appears to be a generic
feature of hole-doped superconductors. Because of bilayer splitting, though,
this doping value is considerably lower than that for the single layer
materials, which again argues that it is unrelated to Tc
Signatures of non-monotonic d-wave gap in electron-doped cuprates
We address the issue whether the data on optical conductivity and Raman
scattering in electron-doped cuprates below support the idea that the
wave gap in these materials is non-monotonic along the Fermi surface. We
calculate the conductivity and Raman intensity for elastic scattering, and find
that a non-monotonic gap gives rise to several specific features in optical and
Raman response functions. We argue that all these features are present in the
experimental data on NdCeCuO and PrCeCuO
compounds.Comment: 7 pages, 6 figure
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