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The article discusses about the research on superconductivity properties of iron selenide monolayer films deposited on strontium titanate at high temperatures. Topics include the compound pnictides and cuprates, the experiments on superconductors, the development of heterostructures, and Fermi surfaces and energy.

Examines the atomic-layer engineering of superconducting oxides. Occurrence of zero-bias conductance anomaly; Growth of superlattices in which thin high-temperature superconductor layers alternate with layers of ferromagnetic oxide; Development of fast, non-volatile memory based either on ferromagnets, including colossal magnetoresistance materials.

The interface layers of La2-xSrxCuO4 (LSCO) thin films epitaxially grown on LaSrAlO4 substrates by molecular beam epitaxy were investigated using transmission electron microscopy (TEM). In single-phase LSCO film, we observed an irregular layering sequence near the interface between the film and the substrate, as well as an abundance of oxygen vacancies in CuO2 layers. A multilayer LSCO film with a high critical temperature (Tc = 44.5 K) showed perfect interfaces between the sublayers. Furthermore, by combining scanning TEM, electron energy-loss spectroscopy, and electron holography, we show that there is little or no interdiffusion between the sublayers. The interfacial defects and oxygen vacancies reduce Tc, while the compressive strain in high-quality multilayers enhances Tc. [ABSTRACT FROM AUTHOR]

Layered perovskite La2CuO4+δ (LCO) thin films were epitaxially grown on SrTiO3 (STO) and LaSrAlO4 substrates by atomic-layer-by-layer molecular beam epitaxy. The lattice defects and residual strain in these films were investigated by means of transmission electron microscopy and electron energy loss spectroscopy. The LCO films showed a high epitaxial quality with flat interfaces and top surfaces. Misfit dislocations with Burgers vector a<010> and shear defects were frequently observed at or near the film/substrate interfaces and in the films, respectively. In one LCO film, grown on STO at the highest temperature, 700 °C, we observed a two layered structure with the top layer being rhombohedral CuLaO2. In addition, stacking faults were observed in the plane views of one LCO film grown on the STO substrate. The residual strains were evaluated from the associated splitting of Bragg reflection. Possible mechanisms of strain relaxations are discussed based on the observed defects. [ABSTRACT FROM AUTHOR]

Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable "structural isosbestic" point and a threshold effect for the dependence of c-axis expansion (Δc) on fluence (F), with Δc/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at ∼0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity. [ABSTRACT FROM AUTHOR]

Abstract: Using an advanced molecular beam epitaxy system for atomic-layer engineering of complex oxides, we have fabricated a variety of superlattices with stacked layers of La2− x Sr x CuO4 doped to different levels. In superlattices formed by stacking highly overdoped, metallic La1.5Sr0.5CuO4 and insulating La2CuO4 layers we have observed superconductivity at temperature as high as 30K, even though neither of the building blocks was superconducting. Different possible mechanisms of this superconductivity are discussed. [Copyright &y& Elsevier]