Thermoelectric power of textured Bi2Sr2CaCu2O8: Evidence for field-induced hysteretic behavior.

Abstract

The thermoelectric power (TEP) of textured ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ has been measured with an ac technique in an applied magnetic field (up to 3 kG). Parallel and perpendicular geometries of the temperature gradient and the magnetic field have been systematically studied. A field-induced hysteretic behavior of the TEP due to the difference between cooling and heating runs is observed. The hysteresis surface versus field curve presents a maximum near 100 G for both geometries. The hysteretic behavior below ${\mathit{T}}_{\mathit{c}}$ is discussed in terms of the intrinsic Josephson effect caused by the formation of Josephson vortices, while above ${\mathit{T}}_{\mathit{c}}$ the hysteresis is attributed to the manifestation of the two-dimensional Gaussian fluctuations of the order parameter. In so doing, the critical-current density is found to behave as ${\mathit{J}}_{\mathit{c}}$\ensuremath{\propto}[1+(H/${\mathit{H}}_{\mathit{J}}$${)}^{2}$${]}^{\mathrm{\ensuremath{-}}1}$. An activation energy, U(T,H), deduced from the Arrhenius plot of the TEP below ${\mathit{T}}_{\mathit{c}}$, shows a linear temperature dependence, U(T)\ensuremath{\approxeq}1-T/${\mathit{T}}_{\mathit{c}}$, a power-law magnetic field dependence, U(H)\ensuremath{\propto}${\mathit{H}}^{\mathrm{\ensuremath{-}}1/4}$, and has the absolute value of ca. 0.5 eV at T=0 and H=50 G. Such a behavior of the observed TEP and the dependences and origin of U(T,H) are argued to be attributed to the highly anisotropic nature of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ layered superconductors.