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.

Fluctuation conductivity in Y–Ba–Cu–O films with artificially produced defects

“…Really, the LD model predicts a smooth, gradual transition from 2D AL fluctuation behavior to 3D AL behavior as the temperature approaches T c , and it considers the MT contribution to be vanishing. This kind of FC behavior has been shown to be typical for badly structured high-T c oxides [2]. However, in most of the previous papers devoted to the problem, FC fitted by the LD model alone is reported [4][5][6][7][8][9], suggesting the presenñå of different structural defects in the samples studied.…”

“…(2), (3) and (7) must be multiplied to fit the experimental data. It is clear that the farther C is from 1, the more influence of defects is expected [2]. However, independently of the measured values of the C factors, the ratio…”

“…T c0 = (100 ± 5) K is the temperature which determines the pair-breaking parameter d th = = -( ) T T /T c c c 0 [12,13]. The possibility of the fluctuating pairing in HTSC at T c0 < T < T *0 is widely debated at present [1][2][3].…”

“…Measurements taken with a wide variety of techniques demonstrate that the pseudogap is present in both the spin and charge channel but theoretical views of the problem are still rather controversial. One point of view which stands out in the context of experimental evidence is the idea of preformed pairs [1] considered to be the fluctuating Cooper pairs which are believed to be present in HTSC well above T c [2,3]. As structural defects are known to deeply affect the pair-breaking mechanism in high-T c oxides [2], investigation of the influence of systematically produced structural defects on the fluctuation conductivity is to clarify the issue.…”

“…The expected strong anisotropy of the scattering of the fluctuating pairs due to growth-related defects influence is revealed. The results are treated using a recently developed approach to FC analysis in YBCO films [2,16].…”