Electrical and Thermal Magneto-Transport in the Mixed State of High T_c-Superconductors

Abstract

The electrical resistivity, thermoelectric power (or Seebeck effect) and thermal conductivity probe the charge and heat carrier currents caused by external electric and temperature gradients. When a magnetic field is additionally superimposed, phenomena called excess electrical resistivity, excess thermoelectric power, Nemst effect and excess electrothermal conductivity can be observed on superconducting samples. This allows one to supply some consistent information on the kinetics of vortices and of quasi particle scattering in the mixed state. It is shown from the electrical resistivity measured with a disk geometry that vortex and quasiparticle dissipations seem to have the same order of magnitude, in contrast to low temperature/conventional superconductors. Before analysing the Seebeck effect in a field, the zero field case should be appropriately understood with respect to having a grasp on the “background term”, in particular for semimetallic-like systems with several carrier bands. The field dependent electrothermal conductivity which is the ratio of the Seebeck coefficient to the electrical resitivity, is finally shown to contain the signature of the order parameter symmetry up to the critical temperature. Therefore much effort should be put on sorting out first the various dissipation mechanisms in the mixed state of superconductors if superconducting microwave devices (in a field) are envisaged. Moreover, it is of interest to have some further thought on the role that an anisotropic d-wave gap parameter can have on microwave properties and how its peculiar symmetry can be used in devices.