M. Houssa et al., SUPERCONDUCTING FLUCTUATIONS IN THE THERMAL-CONDUCTIVITY OF BI2SR2CACU2O8 AND DYBA2CU3O7-X MATERIALS, Physical review. B, Condensed matter, 56(2), 1997, pp. 802-808
The thermal conductivity kappa of Bi2Sr1.8Ca1.2Cu2O8 and DyBa2Cu2O7-x
polycrystals is analyzed near the critical temperature (T-c=79.5 and 8
3.8 K, respectively) in order to extract the superconducting fluctuati
on contribution kappa(fl). The fluctuationless background is calculate
d in a formal way, taking into account both an electronic and a phonon
contribution above and below the critical temperature. The fluctuatio
n contribution to the electronic thermal conductivity is then extracte
d. A crossover from a critical to a Gaussian fluctuation regime (\T-G-
T-c\approximate to 2.2 K) is observed on the Bi2Sr1.8Ca1.2Cu2O8 sample
both above and below T-c, followed by a crossover from a three-dimens
ional (3D) to a 2D Gaussian behavior (\T-VL-T-c\approximate to 3.7 K)
as the sample temperature is further moved away from T-c. On the other
hand, a 3D behavior only is observed on the DyBa2Cu2O7-x material in
the normal and superconducting states. In both systems, the critical e
xponents are found to be those theoretically predicted. Moreover, the
crossover temperatures are consistent with those expected from the dif
ferently anisotropic structures of these compounds. From the crossover
temperatures and the thermal conductivity fluctuation contribution am
plitudes, quite realistic values for the Ginzburg-Landau parameter k(G
L), the interlayer coupling energy J(c), and the electronic mean free
path l(e) near T-c are found in those materials.