Unusual Seebeck and Nernst effects in the mixed state ofBi2−xPb

Abstract

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 ...

Thermal conductivity and thermal Hall effect in Bi- and Y-based high-T c superconductors

“…It is usually obtained from measurements of the Nernst effect (or the Ettingshausen effect) and the flux-flow resistivity [3,25,35,[52][53][54][55]. Φ 0 is the flux quantum and S is the thermopower (or Seebeck-coefficient) [25,35,[53][54][55]. For an estimate we use the data on YBCO of references [54,55]: s v ≈ 5 × 10 −15 J/Km close to T c ≈ 90 K and S(T c ) ≈ 2.5 µV/K.…”

Influence of a non-uniform current density profile on quasiparticle excitations and thermally activated flux creep in YBa2Cu3O7−σ

“…1) is proportional to the distance ¸ -according to ¼ J» L [3][4] . Since for high-¹ A materials the Hall angle " is very small [17], we neglect its influence and suppose hereafter that V "" J;B. A similar proportionality to ¸3 -4 holds for the quasiparticle component of the voltage, namely ¼ q J O L ¸3 -4 , measured on this bar sample ( L is the normal state resistivity).…”

“…Turning now to (17) and (18), for the prefactor of the TAFF expression (see (16)) we obtain finally:…”

Josephson vortex contribution toc-axis thermopower inBi2Sr2Логвенов1, Waldmann2, Kleiner3 et al. 1998Phys. Rev. B0000View full textAdd to dashboardCite

“…While the dynamics of pancake vortices under a temperature gradient has been well investigated, [5][6][7][8][9] the contribution of Josephson vortices to the TEP is still puzzling. In Ref.…”

“…[5][6][7][8][9] The magnetic field was applied perpendicular to the CuO 2 layers. It has been established that the in-plane TEP below T c is caused by the motion of pancake vortices and the TEP was found to be proportional to the flux flow resistivity S m (T,H)ϭ m (T,H)•S n / n , where S m (T,H), S n and m (T,H), n are the TEP coefficients and resistivities in the mixed state and normal state, respectively.…”