No abstract

Using pulsed-laser ablation with an improved oxygen annealing process and Hall effect measurements, we show that the reduction process needed to induce superconductivity in electron-doped cuprates thin films does not trigger a significant change in carrier concentration ͑or band filling͒ contrary to cerium substitution. We show that it has, however, a severe impact on hole-type carrier mobility. This feature is evidenced by focusing on the overdoped regime ͑x Ն 0.16͒ for which reduction increases the contributions of hole-type quasiparticle excitations to the Hall coefficient without affecting much the contribution from electrons. Since reduction has been also shown recently to provoke a strong suppression of antiferromagnetic order for doping close to optimal, we interpret the strong increase in mobility to result from a decreasing scattering rate related to a decreasing strength of antiferromagnetic correlations. We suggest that delocalization of hole-type carriers with reduction is achieved through the frustration of the antiferromagnetic order of as-grown nonsuperconducting composition by in-plane oxygen vacancies. We propose a comparison of ARPES data for as-grown and reduced Pr 2−x Ce x CuO 4 on the overdoped side as a possible experiment to clarify the origin of the hole-type quasiparticles with reduction.

Our laboratory treats guinea pigs with hyperbaric oxygen (HBO) as a model for investigating the formation of nuclear cataract. Previous analyses of lens supernatants using this model have shown an increase in disulfide (-SS-) and loss of sulfhydryl (-SH) in the lens nucleus of O 2 -treated animals. In this paper, we have used the non-invasive technique of Raman spectroscopy to confirm these findings in intact, freshly-excised lenses. Guinea pigs were treated 3 times per week with HBO for a total of 50 (4 months of treatment) or 85 (7 months of treatment) times to induce an increased level of lens nuclear light scattering. Intact lenses were analyzed by Raman spectroscopy using a 514.5 nm laser and collecting the scattered light in a 90° geometry. The laser beam was focused either in the lens nucleus or equatorial cortex. Changes in the levels of -SS-(503 cm −1 ) and -SH (2577 cm −1 ) vibrations were measured. Raman spectra were analyzed by fitting Lorentzian profiles to the observed data in the -SS-and -SH regions. -SS-levels in the O 2 -treated nucleus were found to have increased by a factor of 2.1 (p=0.0001) and 2.5 (p=0.001) after 50 and 85 HBO treatments, respectively, compared to age-matched controls. Based on previous biochemical analyses, the -SSincrease was due mainly to the formation of protein disulfide (PSSP) with contribution also from protein/thiol mixed disulfides, but not from oxidized glutathione. -SH levels in the O 2 -treated nucleus decreased by 13% (p=0.007) and 35% (p=0.001) after 50 and 85 HBO treatments, respectively, compared to age-matched controls. No significant increase in -SS-or loss of -SH was observed in the lens cortex of the O 2 -treated guinea pigs. The Raman spectroscopy results rule out the possibility that artifactual production of -SS-and loss of -SH occurred during homogenization of lenses in previous studies. The data provide additional evidence to support a link between O 2 , disulfidecrosslinking of lens crystallins in the nucleus, and nuclear cataract.

Using magnetoresistance measurements as a function of applied magnetic field and its direction of application, we present sharp angular-dependent magnetoresistance oscillations for the electrondoped cuprates in their low-temperature non-metallic regime. The presence of irreversibility in the magnetoresistance measurements and the related strong anisotropy of the field dependence for different in-plane magnetic field orientations indicate that magnetic domains play an important role for the determination of electronic properties. These domains are likely related to the stripe phase reported previously in hole-doped cuprates.