No abstract

No abstract

We present measurements of the Peltier-effect in the mixed state of Bi,.,,Pb,,SrzCazCu,Od. The Peltier-coefficient broadens in a magnetic field quite similar to the resistivity and the thermopower. Comparison with the thermopower shows that Onsagers relation holds well. The occurrence of the Peltier-heat in the mixed state well below T, implies that the electric current is accompanied by a large heat current. We show that the vortex contribution to the Peltier-heat is negligibly small. Therefore the heat current has to be attributed to normal quasiparticle excitations. Our results indicate that this quasiparticle contribution to the heat current remains large even at temperatures far below c.

Measurements of the Nernst and of the Seebeck coefficient in the mixed state on a polycrystalline sample of Bil 76Pbp p4Sr2Ca2Cu30& are presented for temperatures between '70 and 120 K and magnetic fields up to 5 T. Nernst and Seebeck voltages are both large. The Seebeck voltage is larger by a factor of about 1000 than expected from the conventional flux creep-flow model. It is shown that our results can be understood if in addition to the flux flow-creep mechanism another important mechanism of dissipation is active. A possible mechanism based on fluctuations of the order parameter over internal weak links is discussed.Unusual, strong dissipation is observed in the mixed state of the high-T, superconductors (HTSC). Prominent manifestations of this dissipation are the unusual broadening of the resistive transition in a magnetic field' and relaxation phenomena observed in the magnetization. ' In view of these large effects one expects that therrnomagnetic effects can be observed in the mixed state also.In this paper we present measurements of the Seebeck and the Nernst effect on a polycrystalline sample of Bi2 "Pb"Sr2Ca2Cu30& for temperatures between 70 and 120 K and magnetic fields up to 5 T. We find that both effects are large, the ratio of transverse to longitudinal thermal electrical fields being of order 1. This is inconsistent with a conventional flux creep-flow mechanism as the only source of the dissipation, since in that case one expects the Seebeck effect to be smaller than the Nernst effect by a factor of 1000. We show that our results can be explained, if one assumes that an additional important mechanism of dissipation is active in the mixed state. A possible such mechanism, which is closely related to the presence of internal (intergranular and intragranular) weak links, ' is discussed. The measurements were carried through on one of a series of polycrystalline samples of Bi2,Pb"Sr2Ca2Cu&Os (Bi-Pb-Sr-Ca-Cu-O), which showed reproducible superconducting properties. Sample preparation and characterization as well as a study of the superconducting properties have been presented in Ref. 6. The sample used for the present measurements shows zero resistance in zero magnetic field at Tco Tc(8 =0) 108' 5 K The Seebeck coefficient S and the Nernst-coefficient Q are defined as V TS = Ei and Q (V T X B) = E,( j,& =0), where EI and E, are the longitudinal and transverse components of the electric field with respect to the temperature gradient V T and B is the magnetic field (e.g. , Ref. 7).S and Q were measured as function of magnetic field (swept at about 0.5 T/min) at fixed temperatures stabilized within about 50 rnK with an imposed temperature gradient V T of about 0.5 to 1 K. The arrangement of the sample allowed measurements for VT~~B and for V TlB.The temperature gradient, built by a small heater (manganin; dp/d8 =0) using a constant heating current, was measured via calibrated Pt resistors mounted to the ends of the sample. The magnetic-field dependence of the resistance of Pt in the temperature range of ...

No abstract