ANISOTROPIC SURFACE IMPEDANCE OF YBA2CU3O7-DELTA SINGLE-CRYSTALS

The anisotropic surface resistance Rs-ab and Rs-c as well as the penetration depth ab and c of YBa2Cu3O7- single crystals have been measured at 9.6 GHz. c(T) and ab(T) are linear in temperature at low temperatures with much different slopes, consistent with the existence of line nodes on a cylindrical Fermi surface. A collapse of the c-axis scattering rate below Tc is also observed, and the temperature dependence of the ab plane scattering rate is consistent with quasiparticle-quasiparticle scattering. The behavior of c(T) is not consistent with proximity-effect models, or with cubic dx2+y2-z2 pairing symmetry, but is consistent with a cubic dx2-y2 pairing state. © 1995 The American Physical Society.