1,568 research outputs found
Pressure dependence of the oxygen isotope effect in YBaCuO
We have carried out measurements of the pressure dependence to 1.2 GPa of the
oxygen isotope effect on in the high- superconductor
YBaCuO using a clamp cell in a SQUID magnetometer. This compound
lies close to, but just above, the 1/8 doping point where in
LaSrCuO marked anomalies in isotope effects occur. Both
isotopes show the same very large pressure dependence of with the result
that the isotope exponent remains low (0.08) but increases slightly with
increasing pressure. This is discussed in terms of stripe suppression, a
competing pseudogap and the effect of superconducting fluctuations.Comment: 4 pages, 1 figures, submitted to Phys. Rev.
Thermodynamic properties of Bi2Sr2CaCu2O8 calculated from the electronic dispersion
The electronic dispersion for Bi2Sr2CaCu2O(8+d) has been determined from
angle-resolved photoelectron spectroscopy (ARPES). From this dispersion we
calculate the entropy and superfluid density. Even with no adjustable
parameters we obtain an exceptional match with experimental data across the
entire phase diagram, thus indirectly confirming both the ARPES and
thermodynamic data. The van Hove singularity is crossed in the overdoped region
giving a distinctive linear-in-T temperature dependence in the superfluid
density there.Comment: 5 pages, 4 figures, submitted to Physical Review Letter
Electron pockets and pseudogap asymmetry observed in the thermopower of underdoped cuprates
We calculate the diffusion thermoelectric power of high-Tc cuprates using the
resonating-valence-bond spin-liquid model developed by Yang, Rice and Zhang
(YRZ). In this model, reconstruction of the energy-momentum dispersion results
in a pseudogap in the density of states that is heavily asymmetric about the
Fermi level. The subsequent asymmetry in the spectral conductivity is found to
account for the large magnitude and temperature dependence of the thermopower
observed in underdoped cuprates. In addition we find evidence in experimental
data for electron pockets in the Fermi surface, arising from a YRZ-like
reconstruction, near the onset of the pseudogap in the slightly overdoped
regime.Comment: 6 pages, 7 figures, accepted for publication in EP
Saddle-point van Hove singularity and the phase diagram of high-Tc cuprates
We examine the generic phase behavior of high-Tc cuprate superconductors in
terms a universal van Hove singularity in the strongly overdoped region. Using
a rigid ARPES-derived dispersion we solve the BCS gap equation and show that
the pairing interaction or pairing energy cutoff must be a rapidly declining
function of doping. This result is prejudicial to a phonon-based pairing
interaction and more consistent with a magnetic or magnetically enhanced
interaction.Comment: 5 pages, 2 figures, submitted to Physical Review
Anomalous peak in the superconducting condensate density of cuprate high T_{c} superconductors at a unique critical doping state
The doping dependence of the superconducting condensate density, n_{s}^{o},
has been studied by muon-spin-rotation for
Y_{0.8}Ca_{0.2}Ba_{2}(Cu_{1-z}Zn_{z})_{3}O_{7-\delta} and
Tl_{0.5-y}Pb_{0.5+y}Sr_{2}Ca_{1-x}Y_{x}Cu_{2}O_{7}. We find that n_{s}^{o}
exhibits a pronounced peak at a unique doping state in the slightly overdoped
regime. Its position coincides with the critical doping state where the normal
state pseudogap first appears depleting the electronic density of states. A
surprising correlation between n_{s}^{o} and the condensation energy U_{o} is
observed which suggests unconventional behavior even in the overdoped region.Comment: 10 pages, 3 figure
Absence of an isotope effect in the magnetic resonance in high- superconductors
An inelastic neutron scattering experiment has been performed in the
high-temperature superconductor to search for an
oxygen-isotope shift of the well-known magnetic resonance mode at 41 meV.
Contrary to a recent prediction (I. Eremin, {\it et al.}, Phys. Rev. B {\bf
69}, 094517 (2004)), a negligible shift (at best +0.2 meV) of the
resonance energy is observed upon oxygen isotope substitution
(OO). This suggests a negligible spin-phonon interaction in
the high- cuprates at optimal doping.Comment: 3 figure
The superfluid density in cuprate high-Tc superconductors - a new paradigm
The doping dependence of the superfluid density, r_s, of high-Tc
superconductors is usually considered in the context of the Uemura relation,
namely Tc proportional to rs, which is generally assumed to apply in the
underdoped regime. We show that a modified plot of Tc/Do versus rs, where Do is
the maximum d-wave gap at T=0, exhibits universal features that point to an
alternative interpretation of the underlying physics. In the underdoped region
this plot exhibits the canonical negative curvature expected when a
ground-state correlation competes with superconductivity (SC) by opening up a
gap in the normal-state DOS. In particular rs is suppressed much faster than
Tc/Do or indeed Tc. The pseudogap is found to strongly modify the SC ground
state.Comment: 9 pages, 5 figures, submitted Phys. Rev. Let
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