28 research outputs found
Charge-Inhomogeneity doping relations in YBCO detected by Angle Dependent Nuclear Quadrupole Resonance
The origin of charge inhomogeneity in YBa_{2}Cu_{3}O_{y} is investigated
using a new experimental method designed to determine the nuclear quadrupole
resonance (NQR) asymmetry parameter eta for very wide NQR lines at different
positions on the line. The method is based on the measurement of the echo
intensity as a function of the angle between the radio frequency field H1 and
the principal axis of the electric field gradient. Static charge inhomogeneity
deduced from eta>0 are found in this compound, but only in conjunction with
oxygen deficiency. This limits considerably the possible forms of charge
inhomogeneity in bulk YBa_{2}Cu_{3}O_{y}.Comment: To be published in Phys. Rev. B; Revised version with a correction to
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Universal linear relations between susceptibility and Tc in cuprates
We developed an experimental method for measuring the intrinsic
susceptibility \chi of powder of cuprate superconductors in the zero field
limit using a DC-magnetometer. The method is tested with lead spheres. Using
this method we determine \chi for a number of cuprate families as a function of
doping. A universal linear (and not proportionality) relation between Tc and
\chi is found. We suggest possible explanations for this phenomenon.Comment: Accepted for publication in PR
A magnetic analog of the isotope effect in cuprates
We present extensive magnetic measurements of the
(Ca_xLa_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_{3}O_{y} (CLBLCO) system with its four
different families (x) having a Tc^max(x) variation of 28% and minimal
structural changes. For each family we measured the Neel temperature, the
anisotropies of the magnetic interactions, and the spin glass temperature. Our
results exhibit a universal relation Tc=c*J*n_s for all families, where c~1, J
is the in plane Heisenberg exchange, and n_s is the carrier density. This
relates cuprate superconductivity to magnetism in the same sense that phonon
mediated superconductivity is related to atomic mass.Comment: With an additional inset in Fig.