The role of oxygen vacancies in SrTiO3 at the LaAlO3/SrTiO3 interface

Strontium titanate, SrTiO3, a widely used substrate material for electronic oxide thin film devices, has provided many interesting features. In a combination with a similar oxide material, LaAlO3, it has recently received great interest. It was suggested that two-dimensional electron gas is formed at the interface between SrTiO3 and LaAlO3, resulting in high electrical conductivity and mobility. In this report we demonstrate that the transport properties in those heterostructures are very sensitive to the deposition parameters during thin film growth. Using cathode- and photoluminescence studies in conjunction with measurements of electrical transport properties and microstructure we show that the electronic properties observed at a LaAlO3/SrTiO3 interface can be explained by oxygen reduced SrTiO3. In addition, we demonstrate that oxygen can be pushed in and out of the sample, but that re-oxygenation of an initially oxygen depleted LaAlO3/SrTiO3 heterostructure is partly prevented by the presence of the film.Comment: 19 pages, 5 figure

Operation of a high-T-C SQUID gradiometer with a two-stage MEMS-based Joule-Thomson micro-cooler

Practical applications of high-T-C superconducting quantum interference devices (SQUIDs) require cheap, simple in operation, and cryogen-free cooling. Mechanical cryo-coolers are generally not suitable for operation with SQUIDs due to their inherent magnetic and vibrational noise. In this work, we utilized a commercial Joule-Thomson microfluidic two-stage cooling system with base temperature of 75 K. We achieved successful operation of a bicrystal high-T-C SQUID gradiometer in shielded magnetic environment. The micro-cooler head contains neither moving nor magnetic parts, and thus does not affect magnetic flux noise of the SQUID even at low frequencies. Our results demonstrate that such a microfluidic cooling system is a promising technology for cooling of high-T-C SQUIDs in practical applications such as magnetic bioassays