Fluctuation conductivity in YBa2Cu3O7−y films with different oxygen content. II. YBCO films with Tc≈80 K

Abstract

The fluctuation conductivity in YBa2Cu3O7−y (YBCO) films with T≈80 K is investigated for the first time. Unlike the optimally doped samples, these films exhibit a transition from a Maki–Thompson (MT) mechanism for the scattering of fluctuational pairs to a Lawrence–Doniach (LD) mechanism and, as the temperature approaches Tc, to an Aslamazov–Larkin (AL) mechanism. It is shown that the coherence length ξc(0) along the c axis and the phase relaxation time τφ(100 K) of the fluctuational pairs are determined by the temperature of this second transition. The features observed on both the fluctuation conductivity and resistive behavior are sharply enhanced as Tc approaches 80 K, probably because of a significant increase in the intensity of the magnetic interaction in high-Tc superconductors at these temperatures. In spite of this, for two samples a value τφ(100 K)=(3.35±0.01)×10−13 s is measured, i.e., the same value as for optimally doped YBCO films. It is shown that the dependence of ξc(0) on Tc obeys the standard theory of superconductivity. The mechanisms for the scattering of charge carriers and the superconducting pairing in YBCO are analyzed.