Implantation, damage, and regrowth of high Tc superconductors
Abstract We have observed superconductivity in thin films of (La1−xSrx)2CuOy which are fabricated by implanting evaporated La/Cu multilayer films with Sr and annealing in oxygen. The films are insulating and partially transparent as-implanted, but they darken and become conducting at annealing temperatures as low as 500°C. The resistive behavior is very sensitive to the annealing conditions and the superconducting layer appears to be buried beneath the surface. Similarly, implantation of F, O, and Ne into single crystals and high quality (χmin
Oxygen and rare-earth doping of the 90-K superconducting perovskite YBa2Cu3O7-x.
Structural, magnetic and electronic properties of compounds in the series RBa/sub 2/Cu/sub 3/O/sub 7-//sub x/ (R = Nd,Sm,..., and Lu) were studied. Resistivity, Meissner-effect, and shielding measurements have revealed superconductivity among all the rare-earth compounds, except La, Pr, and Tb, with critical temperatures T/sub c/ measured at the midpoint of the resistive transition ranging from 87 to 95 K. No depression of T/sub c/ was observed upon introduction of most of the rare-earth magnetic ions. Susceptibility measurements down to 1.6 K have shown that an antiferromagnetic ordering (most likely due to dipole-dipole interactions) occurs only for the Gd compound. Changes in oxygen content in these materials drastically affect their physical properties. The importance of the cooling rate during the synthesis of the sample has been correlated to oxygen content. T/sub c/'s are optimized by slow cooling. Annealing at 700/sup 0/C in oxygen pressure of 40 atmospheres slightly increase T/sub c/, while annealing under vacuum at 420/sup 0/C destroys T/sub c/ and induces a semiconducting behavior. These changes in oxygen content and T/sub c/ are perfectly reversible.
Critical current densities and transport in superconducting YBa2Cu3O7−δ films made by electron beam coevaporation
Thin films of the high Tc superconductor YBa2Cu3O7−δ were prepared and characterized. The films made on SrTiO3 showed epitaxial growth and high critical current densities in excess of 9×104 at 78 K and 2×106 at 4.2 K. Also, surface pinning in the parallel direction was found to be very high. The measurements put a lower limit on the depairing critical current density of 5×107 A/cm2.