We report direction-dependent susceptibility and resistivity measurements on La2−xSrxCuO4 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 Tc, 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 Tc is anomalously high.
@article{arxiv.1111.0470,
title = {Parallel and Perpendicular Susceptibility Above $T_{c}$ in La$_{2-x}$Sr$_{x}$CuO$_{4}$ Single Crystals},
author = {Gil Drachuck and Meni Shay and Galina Bazalitsky and Jorge Berger and Amit Keren},
journal= {arXiv preprint arXiv:1111.0470},
year = {2012}
}