Thin films of high-Tc YBCO with frozen strains

Abstract

Strained YBa2Cu3O7−δ (YBCO) films of greater than the critical thickness are grown on LaAlO3 (100) substrates by the method of laser ablation. The strains are frozen in the films by rapid cooling after deposition. These films have an unusual temperature dependence of the critical current density: a characteristic minimum is observed in the temperature interval 55–57 K. The critical current density decreases from 106A∕cm2 at 77 K to 104A∕cm2 and lower. The films are stable against thermocycling from 300 K to the boiling point of liquid nitrogen. It is concluded on the basis of a scanning tunneling microscope study that a macroscopic structuring of the films occurs, with the formation of strain domains. The size of the domains decreases with increasing degree of strain of the films and is, on average, from 1 to 2.4μm. The penetration of magnetic field into a film with frozen strain differs from the penetration into single-crystal and granular films; this also suggests a macroscopic structuring in the strained films.

A Review on Strain Study of Cuprate Superconductors

“…By forming Y124, strain-derived interactions with other defects were concatenated and intrinsic defects were nucleated in YBCO films, resulting in a distributed network of randomly distributed nanostrained regions that profoundly altered vortex-pinning efficiency. K. N. Yugay and A. V. Muravjev [69] used laser ablation to deposit strained YBCO films (thicker than the critical thickness) on LaAlO 3 (100) substrates. By rapidly cooling films after deposition, strains were frozen in films.…”