Abstract:We show that despite the low anisotropy, strong vortex pinning and high irreversibility field H irr close to the upper critical field H c2 of Ba(Fe 1-x Co x ) 2 As 2 , the critical current density J gb across [001] tilt grain boundaries (GBs) of thin film Ba(Fe 1-x Co x ) 2 As 2 bicrystals is strongly depressed, similar to high-T c cuprates. Our results suggest that weak-linked GBs are characteristic of both cuprates and pnictides because of competing orders, low carrier density, and unconventional pairing symmetry. PACS: 74.70.xa, 74.25.F-______________________________________ *

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Understanding new superconductors requires high-quality epitaxial thin films to explore intrinsic electromagnetic properties and evaluate device applications. So far, superconducting properties of ferropnictide thin films seem compromised by imperfect epitaxial growth and poor connectivity of the superconducting phase. Here we report new template engineering using single-crystal intermediate layers of (001) SrTiO(3) and BaTiO(3) grown on various perovskite substrates that enables genuine epitaxial films of Co-doped BaFe(2)As(2) with a high transition temperature (T(c,rho=0) of 21.5 K, where rho=resistivity), a small transition width (DeltaT(c)=1.3 K), a superior critical current density J(c) of 4.5 MA cm(-2) (4.2 K) and strong c-axis flux pinning. Implementing SrTiO(3) or BaTiO(3) templates to match the alkaline-earth layer in the Ba-122 with the alkaline-earth/oxygen layer in the templates opens new avenues for epitaxial growth of ferropnictides on multifunctional single-crystal substrates. Beyond superconductors, it provides a framework for growing heteroepitaxial intermetallic compounds on various substrates by matching interfacial layers between templates and thin-film overlayers.

In recent years, reversible control over metal-insulator transition has been shown, at the nanoscale, in a two-dimensional electron gas (2DEG) formed at the interface between two complex oxides. These materials have thus been suggested as possible platforms for developing ultrahigh-density oxide nanoelectronics. A prerequisite for the development of these new technologies is the integration with existing semiconductor electronics platforms. Here, we demonstrate room-temperature conductivity switching of 2DEG nanowires formed at atomically sharp LaAlo 3 /srTio 3 (LAo/sTo) heterointerfaces grown directly on (001) silicon (si) substrates. The room-temperature electrical transport properties of LAo/sTo heterointerfaces on si are comparable with those formed from a srTio 3 bulk single crystal. The ability to form reversible conducting nanostructures directly on si wafers opens new opportunities to incorporate ultrahigh-density oxide nanoelectronic memory and logic elements into well-established si-based platforms.