Kathleen M. Paget

Penetration depth in oxygen depleted YBCO thin films

Abstract The effect of oxygen depletion on YBCO film is investigated via penetration depth measurements. The T -dependence is measured in high precision for each oxygen concentration. λ ( T / T c )/ λ (0) vs . T / T c for our films is almost identical for different oxygen content. For a fully oxygenated film, it agrees extremely well with the crystal data for T > 25K. 1/λ 2 (0) which is proportional to superfluid density is reduced by factor 10 as T c is reduced to 48K. T c vs . 1/ λ 2 (0) in our result basically reproduces μSR result on bulk by Uemura et al. except the approximately 25% smaller value in 1/λ 2 (0) of film, which can be interpreted as impurity effect in a d -wave superconductor.

Fluctuation effects in the magnetic penetration depth of high-Tc films

We do not find evidence for strong fluctuation effects in the magnetic penetration depth of films of YBCO. While in YBCO crystals it has been found that (lambda) -3(T) is linear in T below Tc over a range of temperatures from 5K to 15K, (lambda) -2(T) is linear over a range of several degrees K just below Tc in YBCO and SmBCO films with very sharp transitions. At low temperatures, we find a T-linear behavior in (lambda) (T) in pure YBCO and SmBCO films. However, we do not find evidence that the T-linear behavior is due to thermal phase fluctuations which should increase in strength as (lambda) (0) increases.

Comparison of chain (Co) and plane (Zn) dopants on charge transport in YBa2Cu3O7 − δ

We report the penetration depth, A, and infrared reflectance of a YBa 2 (Cu 0.97 Co 0.03 ) 3 O 7-δ film from 35 cm -1 to 600 cm -1 and from 10 K to 300 K. Co is a chain dopant in contrast to previous work on Zn which is a plane dopant. The effects of the chain dopants and the plane dopants are similar in the normal state. For example, the reflectance of the 3% Co sample is very similar to 4% Zn sample at 100 K and 300 K. However, in the superconducting state, 3% Co has a high reflectance similar to pure YBa 2 Cu 3 O 7-δ while 4% Zn has a gapless reflectance. The penetration depth of the Co doped sample is close to that of pure YBa 2 Cu 3 O 7-δ while that of the Zn doped film is a factor of five larger.