Pulsed laser ablation: a new route to synthesize novel superconducting compounds as oriented films

Abstract

We report here the significance of the pulsed laser ablation technique in stabilizing strained lattices that do not form by the conventional ceramic method and show that the technique offers unique possibilities to probe the structure property relationship in complicated systems. One of such systems is LuBa₂Cu₃O_7-δ; a systematic investigation of structural (in)stability of its superconducting phase is presented here. Our analysis suggests that the system suffers from internal strain due to lower ionic radius of Lu³⁺; however, the structure can be stabilized only as oriented films on 100 LaAlO₃, 100 SrTiO₃, and 100 MgO, with excellent superconducting properties (J_c ≈5.0×10⁶ A cm^-2 at 77 K). We have also investigated similar compounds having their stability close to their crystallographic limit. The important feature of these metastable phases is that they grow only as oriented films. Free energy of epitaxial growth of strained films are investigated and a simple growth model is proposed based on our observation. Importance of this growth model in explaining the superconductor-normal-metal-superconductor type of junctions, observed in high-T_c superconductors is highlighted.