13 research outputs found
Parallel and Perpendicular Susceptibility Above in LaSrCuO Single Crystals
We report direction-dependent susceptibility and resistivity measurements on
LaSrCuO single crystals. These crystals have rectangular
needle-like shapes with the crystallographic "c" direction parallel or
perpendicular to the needle axis,which, in turn, is in the applied field
direction. At optimal doping we find finite diamagnetic susceptibility above
, namely fluctuating superconductivity (FSC), only when the field is
perpendicular to the planes. In underdoped samples we could find FSC in both
field directions. We provide a phase diagram showing the FSC region, although
it is sample dependent in the underdoped cases. The variations in the
susceptibility data suggest a different origin for the FSC between underdoping
(below 10%) and optimal doping. Finally, our data indicates that the
spontaneous vortex diffusion constant above is anomalously high
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.
Correlation of the superconducting critical temperature with spin and orbital excitations in (CaxLa1− x)(Ba1. 75− xLa 0. 25) Cu3Oy as measured by resonant inelastic x-ray scattering
Electronic spin and orbital (dd) excitation spectra of (CaxLa1−x )(Ba1.75−xLa0.25+x)Cu3Oy samples are measured by resonant inelastic x-ray scattering (RIXS). In this compound, Tc of samples with identical hole dopings is strongly affected by the Ca/Ba substitution x due to subtle variations in the lattice constants, while crystal symmetry and disorder as measured by linewidths are x independent. We examine two extreme values of x and two extreme values of hole-doping content y corresponding to antiferromagnetic and superconducting states. The x dependence of the spin-mode energies is approximately the same for both the antiferromagnetic and superconducting samples. This clearly demonstrates that RIXS is sensitive to the superexchange J even in doped samples. A positive correlation between J and the maximum of Tc at optimal doping (T max c) is observed. We also measured the x dependence of the dxy→dx2−y2 and dxz/yz→dx2−y2 orbital splittings. We infer that the effect of the unresolved d3z2−r2→dx2→y2 excitation on T max c is much smaller than the effect of J. There appears to be dispersion in the dxy→dx2−y2 peak of up to 0.05 eV. Our fitting furthermore indicates an asymmetric dispersion for the dxz/yz→dx2−y2 excitation. A peak at ∼0.8 eV is also observed and attributed to a dd excitation in the chain layer