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.
Superconductivity and hole doping in Pr0.5Ca0.5Ba2Cu3O7- delta thin films.
We have grown superconducting Pr 0.5 Ca 0.5 Ba 2 Cu 3 O 7− δ epitaxial thin films that exhibit a superconducting onset temperature of 43 K with T c (R=0)=34.9 K. This is the first time, to our knowledge, that 1:2:3-phase superconductivity has been achieved by substituting Ca for Pr, without the presence in the alloy of Y or any other rare-earth element R for which RBa 2 Cu 3 O 7− δ is superconducting. This result supports the view that hole localization/filling contributes substantially to the suppression of superconductivity by Pr in PrBa 2 Cu 3 O 7− δ, and clearly demonstrates that this suppression can be compensated by appropriate hole doping with Ca
Upper critical field and normal-state properties of single-phase Y1-xPrxBa2Cu3O7- gamma compounds.
Substitution of Pr for Y in the Y{sub 1{minus}{ital x}}Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} system depresses {ital T}{sub {ital c}}, with superconductivity disappearing for {ital x}{ge}0.5. The origin of this {ital T}{sub {ital c}} depression is still controversial, as is the valence state of the Pr ion. In order to study these problems, single-phase materials were prepared with {ital x}=0.0, 0.1, 0.2, 0.3, 0.35, 0.4 0.45, 0.5, 0.6, 0.7, 0.9, and 1.0. Under certain annealing conditions, these types of samples will phase separate into YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} and Y{sub 1{minus}{ital x}}Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, showing two transitions in the magnetization, but will still appear single phase from x-ray diffraction. We have overcome this problem through specific annealing conditions of time, temperature, and atmosphere. We find that the superconductivity is strongly suppressed as a function of Pr concentration, with a behavior which is consistent with the classical Abrikosov-Gor'kov pair-breaking theory. The critical fields versus {ital T} show a bell''-shaped behavior, which is consistent with the presence of magnetic pair-breaking interactions. The measured temperature dependence of the critical field, {ital H}{sub {ital c}2} near {ital T}{sub {ital c}}, and the Pauli susceptibility, are used to estimate the physicalmore » parameters {lambda}{sub GL}, {xi}{sub GL}, and {gamma}.« less