1,279 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
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
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
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
Phenomenological theory of the underdoped phase of a high-T superconductor
We model the Fermi surface of the cuprates by one-dimensional nested parts
near and and unnested parts near the zone diagonals.
Fermions in the nested regions form 1D spin liquids, and develop spectral gaps
below some , but superconducting order is prevented by 1D phase
fluctuations.
We show that the Josephson coupling between order parameters at and
locks their relative phase at a crossover scale . Below
, the system response becomes two-dimensional, and the system displays
Nernst effect. The remaining total phase gets locked at , at
which the system develops a (quasi-) long-range superconducting order.Comment: 4 pages, 1 figure; typos corrected, references adde
Competition between antiferromagnetism and superconductivity, electron-hole doping asymmetry and "Fermi Surface" topology in cuprates
We investigate the asymmetry between electron and hole doping in a 2D Mott
insulator, and the resulting competition between antiferromagnetism (AF) and
d-wave superconductivity (SC), using variational Monte Carlo for projected wave
functions. We find that key features of the T = 0 phase diagram, such as
critical doping for SC-AF coexistence and the maximum value of the SC order
parameter, are determined by a single parameter which characterises the
topology of the "Fermi surface" at half filling defined by the bare
tight-binding parameters. Our results give insight into why AF wins for
electron doping, while SC is dominant on the hole doped side. We also suggest
using band structure engineering to control the parameter for enhancing SC.Comment: 4 pages, 4 figure
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