PINNING AND THE MIXED-STATE THERMOMAGNETIC TRANSPORT PROPERTIES OF YBA2CU3O7-DELTA

We have studied the role of pinning in the mixed-state thermomagnetic transport properties of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. We demonstrate the pinning independence of the transport entropy {ital S}{sub {phi}}, and its consequent scaling within an anisotropic mass model. Due to the anisotropy of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} the extrinsic pinning strength effectively decreases as we rotate the magnetic field into the {ital ab} plane. The Nernst ({ital E}{sub {ital y}}/{nabla}{sub {ital xT}}) and Seebeck ({ital E}{sub {ital x}}/{nabla}{sub {ital xT}}) effects are enhanced as we reduce the effective pinning, yet the transport entropy {ital S}{sub {phi}}{proportional_to}({ital E}{sub {ital y}}/{nabla}{sub {ital xT}})/{rho}{sub {ital xx}}, the ratio of the Nernst and Seebeck signals, and the ratio of Seebeck and longitudinal resistivity {rho}{sub {ital xx}} are {ital unchanged}, similar to the pinning independence observed for the Hall conductivity {sigma}{sub {ital xy}}. These results can be explained within a simple phenomenological model of vortex dynamics. {copyright} {ital 1996 The American Physical Society.}