The role of epitaxial strain in the properties of high Tc thin films

Abstract

The difference observed between the critical temperatures measured for bulk material or very thick films (> 500 nm for the ‘214’ system) and those measured for thin films (< 65 nm) has long been of curiosity. Thin films never attain the high values of Tc achieved in bulk or thick film material. Various mechanisms have been proposed to explain this phenomenon, for example Kosterlitz-Thouless effects, inadequate or unstable oxygenation, and strain itself. Formally the role of strain has remained insubstantiated.The system on which we have concentrated our efforts is that of La2-xSrxCuO4 (LSCO) deposited using MBE, mainly onto (001) SrTiO3 (STO) substrates. These films have been grown at about 700°C at ~3 × 10-6 torr oxygen pressure and cooled after growth at -10° min-1. The films have subsequently been examined using several microstructural and electronic probes, including x-ray diffraction, AFM, resistivity, Hall effect and kinetic inductance.