Fluctuation-enhanced conductivity in YBa2Cu2Ox (6.5 <= x <= 6.95) and Tl2Ba2Ca2Cu3O10 +/-delta

Abstract

The fluctuation-induced conductivity (Delta sigma(T)) near T-c of a sole YBa2Cu3Ox (YBCO) film with various precisely controlled oxygen contents (6.5 less than or equal to x less than or equal to 6.95) was studied and compared with those obtained from its Tl-based counterparts. For YBCO films with x > 6.7, Delta sigma (T) displays a distinct 3D to 2D crossover as the temperature approaches T-c. On the other hand, as T -->T-c, Delta sigma (T) of both Tl-based and YBCO film with x less than or equal to 6.7 exhibits a reversed 2D to 3D crossover. It is suggestive that the coupling between the CuO2 layers may have changed significantly with reducing oxygen. (C) 2000 Elsevier Science B.V. All rights reserved.