Anisotropy of superconductivity in an untwinned YBa2Cu3O7 single crystal

The torque curves of a detwinned YBa2Cu3O7 single crystal are reversible under mu(0)H = 0.8 T and T = 90 K for the three different rotation axes. The effective mass model of the torque gives the anisotropy parameters as gamma(ca) = root m(c)/m(a) = 7.55 +/- 0.63 and gamma(cb) = root m(c)/m(b) = 8.95 +/- 0.76. The a-b anisotropy parameter can be obtained as gamma(ab) = root m(a)/m(b) = gamma(cb)/gamma(ca) = 1.18 +/- 0.14. The torque curve in the a-b-plane contains four-fold symmetry.