Atomic-layer engineering of cuprate superconductors

A review of molecular beam epitaxy of ferroelectric BaTiO3 films on Si, Ge and GaAs substrates and their applications

SrTiO3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide-semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Finally, we review the last developments in two areas of interest for the applications of BaTiO3 films on silicon, namely integrated photonics, which benefits from the large Pockels effect of BaTiO3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric.

Epitaxial Oxide Films

Some perspective concerning the capabilities and potential of epitaxial oxide films is gained by comparison with the field of semiconductor epitaxy. The specific epitaxial behavior of MgO, (ZrY)O2, and the layered cuprates is discussed. A suggestion is given for a method of searching for higher temperature superconductors by the use of epitaxial indusions in layered structures.

Giant proximity effect in a phase-fluctuating superconductor

When a tunneling barrier between two superconductors is formed by a normal material that would be a superconductor in the absence of phase fluctuations, the resulting Josephson effect can undergo an enormous enhancement. We establish this novel proximity effect by a general argument as well as a numerical simulation and argue that it may underlie recent experimental observations of the giant proximity effect between two cuprate superconductors separated by a barrier made of the same material rendered normal by severe underdoping.

Giant proximity effect in cuprate superconductors

Using an advanced molecular beam epitaxy system, we have reproducibly synthesized atomically smooth films of high-temperature superconductors and uniform trilayer junctions with virtually perfect interfaces. We found that supercurrent runs through very thick barriers. We can rule out pinholes and microshorts; this "giant proximity effect" (GPE) is intrinsic. It defies the conventional explanation; it might originate in resonant tunneling through pair states in an almost-superconducting barrier. GPE may also be significant for superconducting electronics, since thick barriers are easier to fabricate.

SCIENCE AND TECHNOLOGY OF HIGH-TEMPERATURE SUPERCONDUCTING FILMS

▪ Abstract  The field of high-temperature superconducting thin films is reviewed, focusing on the synthesis and properties of materials that are most promising for device applications. Current materials issues that are important for emerging device applications of oxide superconducting films are discussed, with emphasis on the growth, characterization, and use of epitaxial films. The status of specific superconducting device technologies is briefly reviewed.