Investigation of the anisotropy of dissipation processes in single   crystal of Yba2Cu3O7-d system
  By means of contactless mechanical method of the measurement of energy losses in superconductors, the anisotropy of dissipation processes has been studied in single crystal high-temperature layered superconductors of Yba2Cu3O7-d system, being in mixed state. The observed anisotropy of energy losses indicates the possibility of the existence of the symmetry of order parameter of dx2-y2 type in these single crystals. 
J.G.Chigvinadze, A.A. Iashvili, J.V. Acrivos, T.V. Machaidze, T.Wolf