Indications of superconductivity at somewhat elevated temperatures in strontium titanate subjected to high electric fields

Insulating single-crystal SrTiO₃ wafers have been rendered conductive below room temperature by subjecting them to electric fields. With moderate fields the process can be reversed by warming the substrates to room temperature or slightly above. At higher fields the process is not reversible. When substrates subjected to high fields are cooled to temperatures in the range of 2-6 K, they exhibit significant and sharp resistance drops that respond to magnetic field in a manner suggestive of the presence of superconductivity despite the fact that the resistance does not fall to zero. If these effects are indeed indications of superconductivity they are occurring at temperatures in excess of those found employing techniques previously used to induce superconductivity in SrTiO₃ . The phenomenon is sample dependent and is not observed in every sample. We suggest that these effects are the result of static electric fields producing a redistribution of oxygen vacancies and possibly irreversible structural changes leading to channels that are sufficiently doped so as to be superconducting. The reason the onset temperatures for this effect are higher than those achieved using more conventional doping approaches is an open question.