Pairing Symmetry in Single-Layer Tetragonal Tl(2)Ba(2)CuO(6+delta) from In-Plane Torque Anisotropy

The in-plane torque anisotropy of the high-Tc cuprate Tl(2)Ba(2)CuO(6+delta) gives evidence of a mixed s+d pairing state allowed by the possible breaking of its tetragonal symmetry at low temperature. The validity of our resu lt is supported by the absence of any in-plane anisotropy in the classical superconductors NbN and the layered 2H-NbSe(2) measured under the same conditions.