181 research outputs found
Evidence for pairing above Tc from the dispersion in the pseudogap phase of cuprates
In the underdoped high temperature superconductors, instead of a complete
Fermi surface above Tc, only disconnected Fermi arcs appear, separated by
regions that still exhibit an energy gap. We show that in this pseudogap phase,
the energy-momentum relation of electronic excitations near E_F behaves like
the dispersion of a normal metal on the Fermi arcs, but like that of a
superconductor in the gapped regions. We argue that this dichotomy in the
dispersion is hard to reconcile with a competing order parameter, but is
consistent with pairing without condensation
Protected nodes and the collapse of the Fermi arcs in high Tc cuprates
Angle resolved photoemission on underdoped Bi2Sr2CaCu2O8 reveals that the
magnitude and d-wave anisotropy of the superconducting state energy gap are
independent of temperature all the way up to Tc. This lack of T variation of
the entire k-dependent gap is in marked contrast to mean field theory. At Tc
the point nodes of the d-wave gap abruptly expand into finite length ``Fermi
arcs''. This change occurs within the width of the resistive transition, and
thus the Fermi arcs are not simply thermally broadened nodes but rather a
unique signature of the pseudogap phase.Comment: Accepted by Phys. Rev. Let
Modeling the Fermi arc in underdoped cuprates
Angle resolved photoemission data in the pseudogap phase of underdoped cuprates have revealed the presence of a truncated Fermi surface consisting of Fermi arcs. We compare a number of proposed models for the arcs and find that the one that best models the data is a d-wave energy gap with a lifetime broadening whose temperature dependence is suggestive of fluctuating pairs
Non-dispersive Fermi arcs and absence of charge ordering in the pseudogap phase of Bi2Sr2CaCu2O8+d
The autocorrelation of angle resolved photoemission data from the high
temperature superconductor Bi2Sr2CaCu2O8+d shows distinct peaks in momentum
space which disperse with binding energy in the superconducting state, but not
in the pseudogap phase. Although it is tempting to attribute a non-dispersive
behavior in momentum space to some ordering phenomenon, a de-construction of
the autocorrelation reveals that the non-dispersive peaks arise not from
ordering, but rather from the tips of the Fermi arcs, which themselves do not
change with binding energy.Comment: 4 pages, 3 figure
q-Newton binomial: from Euler to Gauss
A counter-intuitive result of Gauss (formulae (1.6), (1.7) below) is made
less mysterious by virtue of being generalized through the introduction of an
additional parameter
Specific Heat and Superfluid Density for Possible Two Different Superconducting States in NaxCoO2.yH2O
Several thermodynamic measurements for the cobaltate superconductor,
NaxCoO2.yH2O, have so far provided results inconsistent with each other. In
order to solve the discrepancies, we microscopically calculate the temperature
dependences of specific heat and superfluid density for this superconductor. We
show that two distinct specific-heat data from Oeschler et al. and Jin et al.
are reproduced, respectively, for the extended s-wave state and the p-wave
state. Two different superfluid-density data are also reproduced for each case.
These support our recent proposal of possible two different pairing states in
this material. In addition, we discuss the experimentally proposed large
residual Sommerfeld coefficient and extremely huge effective carrier mass.Comment: 5 pages, 4 figures, Submitted to J. Phys. Soc. Jp
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