Anisotropic superconducting properties of Ba2YCu

Abstract

The upper critical magnetic field ${H}_{c2}$ of ${\mathrm{Ba}}_{2}\mathrm{Y}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}y}$ single crystals is estimated from the resistive transition curves as a function of temperature and field direction. ${H}_{c2}$ exhibits a large anisotropy between the $c$ axis and the $a\ensuremath{-}b$ plane. The ${H}_{c2}$ data have linear temperature dependence, giving well-defined $\frac{d{H}_{c2}}{\mathrm{dT}}$ values: -0.56 T/K for the $c$ axis and -3.3 T/K for the $a\ensuremath{-}b$ plane. The angular dependence of ${H}_{c2}$ is in good agreement with the effective-mass model when the ratio $\frac{{M}_{\ensuremath{\perp}}}{{M}_{\ensuremath{\parallel}}}=60$, which is comparable to resistivity anisotropy in the normal state. On the other hand, no signs of anisotropy in the $a\ensuremath{-}b$ plane can be recognized. This indicates that supercurrent flows dominantly in the Cu-O sheets, and that the Cu-O chains with oxygen deficiency are less conductive.