We investigate the ${\text{LaAlO}}_3/{\text{SrTiO}}_3$ interface by means of aberration-corrected ultrahigh-resolution transmission electron microscopy allowing us to measure the individual atomic shifts in the interface at a precision of a few picometers. We find that the oxygen octahedron rotation typical for rhombohedral ${\text{LaAlO}}_3$ is across the interface and is also induced in the originally cubic ${\text{SrTiO}}_3$ layer. Octahedra distortion leads to ferroelectricitylike dipole formation in the interface which is in addition modified by cation intermixing.

In this paper, we review the preparation technology, integration in measurement systems and tests of high-T c superconducting quantum interference devices (SQUIDs) intended for biomagnetic applications. A focus is on developments specific to Forschungszentrum Jülich GmbH, Chalmers University of Technology, MedTech West, and the University of Gothenburg, while placing these results in the perspective of those achieved elsewhere. Sensor fabrication, including the deposition and structuring of epitaxial oxide heterostructures, materials for substrates, epitaxial bilayer buffers, bicrystal and step-edge Josephson junctions, and multilayer flux transformers are detailed. The properties of the epitaxial multilayer high-T c direct current SQUID sensors, including their integration in measurement systems with special electronics and liquid nitrogen cryostats, are presented in the context of biomagnetic recording. Applications that include magnetic nanoparticle based molecular diagnostics, magnetocardiography, and magnetoencephalography are presented as showcases of high-T c biomagnetic systems. We conclude by outlining future challenges.

We have investigated the microstructural and electron transport properties of 45° step-edge Josephson junctions grown on MgO substrates and used them for the preparation of superconducting quantum interference device (SQUID) magnetometers intended for magnetoencephalography (MEG) measurement systems. The high- T _c SQUID magnetometers also incorporate 16 mm multilayer superconducting flux transformers on the MgO substrates and demonstrate a magnetic field resolution of ~ 4 fT/√Hz at 77 K. Results are illustrated for the detection of auditory evoked magnetic responses of the human cortex and compared between high- T _c SQUIDs and a commercial low- T _c MEG system. Our results demonstrate that MEG systems can be upgraded using high- T _c SQUIDs to make them independent of helium and more user-friendly, saving operating costs and leading to the widespread utilization of MEG systems in clinical practice and at universities.

A technique of ultraviolet photolithography of YBa₂Cu₃O_7−x and PrBa₂Cu₃O_7−x films combined with nonaqueous Br‐ethanol chemical etching was developed. Josephson junctions, interconnects, and crossovers on the basis of chemically etched edges of c‐axis oriented YBa₂Cu₃O_7−x thin films were prepared and investigated. For the Josephson junctions with a PrBa₂Cu₃O_7−x barrier, the I_cRn product values of about 10 mV at 4.2 K and up to about 0.6 mV at 77 K were achieved. Shapiro steps were observed in the temperature range up to about 89 K. Critical current spreads of about ±10% were observed. At 77 K, the electrodes of crossovers carried more than 10⁶ A/cm². For a 160‐nm‐thick SrTiO₃ intermediate layer in crossovers, a resistivity of more than 10⁹ Ω cm was achieved at T≤100 K.

The atomic structure of the interfaces of Josephson junctions formed by epitaxial YBa₂Cu₃O₇/PrBa₂Cu₃O₇/YBa₂Cu₃O₇ triple‐layer films was investigated by high‐resolution transmission electron microscopy. The samples were fabricated by sputter deposition on surfaces which were etched ex situ either chemically, using a nonaqueous Br‐ethanol solution, or by an Ar ion beam. In the interfaces produced after ion etching a thin intermediate layer with a thickness of a few nanometers was observed. The main part of this layer consists of cubic PrBa₂Cu₃O₇ or YBa₂Cu₃O₇ which is cation disordered. The interfaces formed during deposition on Br‐ethanol‐etched surfaces did not contain such an intermediate layer but exhibited high structural perfection similar to that of interfaces produced in situ. These observations permit a qualitative explanation of the difference in the electrical properties of junctions produced by these two techniques.