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

The thermoelectric power (TEP) of textured Bi2Sr2CaCu2O8 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 Tc is discussed in terms of the intrinsic Josephson effect caused by the formation of Josephson vortices, while above Tc 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 Jc[1+(H/HJ)2]-1. An activation energy, U(T,H), deduced from the Arrhenius plot of the TEP below Tc, shows a linear temperature dependence, U(T)1-T/Tc, a power-law magnetic field dependence, U(H)H-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 Bi2Sr2CaCu2O8 layered superconductors. © 1993 The American Physical Society.