Insights from the study of high-temperature interface superconductivity

Abstract

A brief overview is given of the studies of high-temperature interface superconductivity based on atomic-layer-by-layer molecular beam epitaxy (ALL-MBE). A number of difficult materials science and physics questions have been tackled, frequently at the expense of some technical tour de force, and sometimes even by introducing new techniques. ALL-MBE is especially suitable to address questions related to surface and interface physics. Using this technique, it has been demonstrated that high-temperature superconductivity can occur in a single copper oxide layer-the thinnest superconductor known. It has been shown that interface superconductivity in cuprates is a genuine electronic effect-it arises from charge transfer (electron depletion and accumulation) across the interface driven by the difference in chemical potentials rather than from cation diffusion and mixing. We have also understood the nature of the superconductorinsulator phase transition as a function of doping. However, a few important questions, such as the mechanism of interfacial enhancement of the critical temperature, are still outstanding.

Cooper-like Pairing and Energy Gap Induced by Ion Electronic Polarizability

“…4). The fact that the pair distance is very small and depends only on very short distance interactions may also help explain very interesting recent observations of high Tc superconductivity in ultrathin films [28].…”

Design of Complex Oxide Interfaces by Oxide Molecular Beam Epitaxy

“…It is also shown that the superconducting transition temperature depends on the layer sequence of the M, I, and superconducting (S) layers. Further details can be found in the reviews devoted to this HT-IS phenomenon [86,95,96] and the original references therein. Herewith, we summarize the main findings and conclusions:…”

High Temperature Interface Superconductivity

“…In this section we review early results as well as data up to about a few years ago on HT-IS. Additional information can be found in several previously published reviews [4,10]. The first results on HT-IS in cuprates were obtained by J. Eckstein and I. Bozovic at Varian Research in California [7] only a few years after the discovery of HTS materials [11].…”

“…Multi-layers made out of copper-oxide based high temperature superconductors (HTS) or those made of band or Mott-type insulating oxides with perovskite-like structures, e.g. LaAlO 3 /SrTiO 3 (LAO/STO) are among the most prominent realizations in the field [3][4][5][6]. A second method is to intervene post-growth and change the properties of a surface or interface layer by applying an external agent, for example by exposure to a chemically reactive environment or by applying a voltage bias to the hetero-structure.…”