The role of interfacial defects in enhancing the critical current density ofYBa2Cu3O7−δ coatings

Abstract

The critical current density (Jc) of very thin YBa2Cu3O7−δ (YBCO) filmscan approach 10 MA cm−2 at 77 K inself-field, but for such films Jc drops sharply as the film thickness is increased. We have shown previouslythat this strong thickness dependence results from an enhancement ofJc near the film–substrate interface. In the present paper we investigateinterfacial enhancement using laser-deposited YBCO films onNdGaO3 substrates, and find that we can adjust deposition conditions to switch the enhancement onand off. We find that the ‘on’ state is accompanied by a dense array of interfacial misfitdislocations, while we do not observe dislocations in films prepared in the ‘off’state. This result appears to be but one of many examples in which interfacialproperties of electronic film materials are profoundly affected by stress-induced defectsat the film–substrate interface; however, to our knowledge the present work isthe only case in which electronic properties are shown to be enhanced by suchdefects.