Supercurrent through grain boundaries in the presence of strong correlations

Strong correlations are known to severely reduce the mobility of charge carriers near half-filling and thus have an important influence on the current carrying properties of grain boundaries in the high-$T_c$ cuprates. In this work we present an extension of the Gutzwiller projection approach to treat electronic correlations below as well as above half-filling consistently. We apply this method to investigate the critical current through grain boundaries with a wide range of misalignment angles for electron- and hole-doped systems. For the latter excellent agreement with experimental data is found. We further provide a detailed comparison to an analogous weak-coupling evaluation.Comment: 4 pages, 3 figure

Dopants adsorbed as single atoms prevent degradation of catalysts

The design of catalysts with desired chemical and thermal properties is viewed as a grand challenge for scientists and engineers. For operation at high temperatures, stability against structural transformations is a key requirement. Although doping has been found to impede degradation, the lack of atomistic understanding of the pertinent mechanism has hindered optimization. For example, porous gamma-Al2O3, a widely used catalyst and catalytic support, transforms to non-porous alpha-Al2O3 at ~1,100C. Doping with La raises the transformation temperature to ~1,250C, but it has not been possible to establish if La atoms enter the bulk, adsorb on surfaces as single atoms or clusters, or form surface compounds. Here, we use direct imaging by aberration-corrected Z-contrast scanning transmission electron microscopy coupled with extended X-ray absorption fine structure and first-principles calculations to demonstrate that, contrary to expectations, stabilization is achieved by isolated La atoms adsorbed on the surface. Strong binding and mutual repulsion of La atoms effectively pin the surface and inhibit both sintering and the transformation to alpha-Al2O3. The results provide the first guidelines for the choice of dopants to prevent thermal degradation of catalysts and other porous materials.Comment: RevTex4, 4 pages, 4 JPEG figures, published in Nature Material

Direct Observation of an Interface Dipole between Two Metallic Oxides Caused by Localized Oxygen Vacancies

Oxygen vacancies are increasingly recognized to play a role in phenomena observed at transition-metal oxide interfaces. Here we report a study of SrRuO3/La0.7Sr0.3MnO3 (SRO/LSMO) interfaces using a combination of quantitative aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, and density-functional calculations. Cation displacements are observed at the interface, indicative of a dipole-like electric field even though both materials are nominally metallic. The observed displacements are reproduced by theory if O vacancies are present in the near-interface LSMO layers. The results suggest that atomic-scale structural mapping can serve as a quantitative indicator of the presence of O vacancies at interfaces

Issues of ideology in English language education worldwide: an overview

The relatively limited consideration of ideology in mainstream theory and research of teaching the English language to speakers of other languages has arguably prevented the problematization of many taken-for-granted perceptions and practices of the field. In this article I attempt to bring part of this marginalized body of scholarship on issues of ideology in the area of English language teaching (ELT) to highlight its potential insights for the field. The article sets out from a view of ideology as the most fundamental beliefs in any social practice, which may provide a less-formidable conception of the term and lessen the divergence among the minority of ELT researchers and professionals that do concern themselves with ideology. Then, after a brief sketch of the notion of ideology of language (education), I present an overview of aspects of this marginal but vibrant stream of thought on issues of ideology in ELT worldwide. Overall, the discussion is aimed to act as a call for the further understanding and embracement of sociopolitically-sensitive and ideologically-informed approaches to ELT theory, research, and practice