Growth and superconducting transition of epitaxial thin films
thin films have been grown on SrTiO3 (STO) and yttrium-stabilized ZrO2 (YSZ) substrates by pulsed laser ablation. The substrate temperature dependence of orientation and superconducting properties were systematically studied. Good quality c-axis and a-axis orientated films can be obtained on SrTiO3 solely by changing the substrate temperature. On YSZ, films with good c-axis orientation can be grown, while it is hard to grow films with good a-axis orientation by changing substrate temperature alone. The highest TC 0 is about 37 K, which is found in the films grown on YSZ with a good c-axis orientation. For the films grown on STO, however, the highest TC 0 is about 35.6 K, with a mixed orientation of c-axis and a-axis. In most of the superconducting films, the weak temperature dependence of the normal state resistivity, as characterized by small ratios, together with a weak localization behaviour just above TC, could be attributed to the essential scattering due to the localized electronic states. The superconducting transitions in a field up to 10 T along the c-axis have been measured on a c-axis oriented film grown on SrTiO3. The zero-temperature in-plane upper critical field BC 2ab(0) is estimated from the resistivity transition data.
Hopping conductivity in fully oxygenated PrBa2Cu3Oy, YBa2Cu2CoOy, and PrBa2Cu2CoOy.
We report results of a comparative study of three nonmetals related to the 1-2-3 cuprate superconductors: fully oxygenated ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ (PBCO), ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{2}$${\mathrm{CoO}}_{\mathit{y}}$ (YBCCO), and ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{2}$${\mathrm{CoO}}_{\mathit{y}}$ (PBCCO). We measured the resistivity up to 300 K and the absolute thermopower (TEP) up to 400 K. The temperature dependence of the resistivity follows the Mott variable-range-hopping (VRH) law \ensuremath{\rho}=${\mathrm{\ensuremath{\rho}}}_{0}$exp(${\mathit{T}}_{0}$/T${)}^{1/4}$ in PBCO up to \ensuremath{\sim}100 K and in the other two systems at least up to room temperature. The results of the TEP measurements show that in YBCCO and in PBCCO the VRH probably takes place via energy states lying mainly below the chemical potential, while in PBCO this process utilizes states lying symmetrically on both sides of the chemical potential. In PBCO the TEP exhibits a cusp at low temperatures that is probably associated with the N\'eel point of the Pr sublattice. In PBCCO we found at low temperatures a sharp sign reversal of the TEP, from p type at high temperatures to n type at low temperatures, which needs further investigation.
Stereoselective interaction between the R enantiomer of warfarin and cimetidine.
The stereoselectivity of the pharmacokinetic interaction between warfarin and cimetidine was investigated in eight healthy volunteers. The warfarin enantiomers were given separately as single doses (15 mg) alone and during chronic administration of cimetidine (1 g day-1). Cimetidine did not interact with S warfarin but there was an interaction with the R enantiomer of warfarin. Cimetidine caused a significant increase in the mean plasma half-life of R warfarin (from 47.8 h to 57.8 h) and a significant decrease in its mean plasma clearance (from 2.3 to 1.7 ml h-1 kg-1) (P less than 0.02). Administration of a pharmacological dose of vitamin K1 together with the enantiomers of warfarin was necessary clinically and resulted in elevation of vitamin K1 2,3-epoxide concentrations, which were similar in each case.