RESUMO
A recent theoretical study [Phys. Rev. B 85, 121411(R) (2012)] predicted a thickness limit below which ideal polar cuprates turn nonpolar driven by the associated electrostatic instability. Here we demonstrate this possibility by inducing a structural transformation from the bulk planar to chainlike structure upon reducing the SrCuO2 repeat thickness in SrCuO2/SrTiO3 superlattices with unit-cell precision. Our results, based on structural investigation by x-ray diffraction and high resolution scanning transmission electron microscopy, demonstrate that the oxygen sublattice can essentially be built by design. In addition, the electronic structure of the chainlike structure, as studied by x-ray absorption spectroscopy, shows the signature for preferential hole occupation in the Cu 3d(3z2-r2) orbital, which is different from the planar case.
RESUMO
The perovskite SrTiO3-LaAlO3 structure has advanced to a model system to investigate the rich electronic phenomena arising at polar oxide interfaces. Using first principles calculations and transport measurements we demonstrate that an additional SrTiO3 capping layer prevents atomic reconstruction at the LaAlO3 surface and triggers the electronic reconstruction at a significantly lower LaAlO3 film thickness than for the uncapped systems. Combined theoretical and experimental evidence (from magnetotransport and ultraviolet photoelectron spectroscopy) suggests two spatially separated sheets with electron and hole carriers, that are as close as 1 nm.
Assuntos
Encéfalo/diagnóstico por imagem , Encéfalo/patologia , Dissecação da Artéria Carótida Interna/complicações , Dissecação da Artéria Carótida Interna/diagnóstico , Estenose das Carótidas/complicações , Estenose das Carótidas/diagnóstico , Transtornos de Enxaqueca/diagnóstico , Distúrbios do Paladar/diagnóstico , Distúrbios do Paladar/etiologia , Adulto , Angiografia Cerebral , Transtornos de Deglutição/diagnóstico , Transtornos de Deglutição/etiologia , Síndrome de Horner/diagnóstico , Humanos , Hipertensão/diagnóstico , Hipertensão/fisiopatologia , Imageamento por Ressonância Magnética , Masculino , Índice de Gravidade de Doença , Tomografia Computadorizada por Raios XRESUMO
Highly strained BiFeO3 films transition into a true tetragonal state at 430 °C but remain polar to much higher temperatures (â¼800 °C). Piezoelectric switching is only possible up to 300 °C, i.e., at temperatures for which strain stabilizes the stripe-like coexistence of multiple polymorphs.
RESUMO
Two patients with craniopharyngioma presenting with the "optic tract edema sign" are described. This sign is seen in a majority of craniopharyngiomas and can be of help in the differentiation with other suprasellar masses such as pituitary adenomas, meningiomas, germinomas and lymphomas. Nevertheless it has to be emphasized that the sign is not absolute and can be seen now and then in these other tumors.
Assuntos
Craniofaringioma/patologia , Edema/patologia , Imageamento por Ressonância Magnética/métodos , Neoplasias Hipofisárias/patologia , Vias Visuais/patologia , Adolescente , Adulto , Craniofaringioma/cirurgia , Diagnóstico Diferencial , Feminino , Humanos , Hipófise/patologia , Hipófise/cirurgia , Neoplasias Hipofisárias/cirurgiaAssuntos
Encéfalo/patologia , Cistos/complicações , Cistos/diagnóstico , Doenças Desmielinizantes Hereditárias do Sistema Nervoso Central/complicações , Doenças Desmielinizantes Hereditárias do Sistema Nervoso Central/diagnóstico , Megalencefalia/etiologia , Diagnóstico Diferencial , Humanos , Lactente , Imageamento por Ressonância Magnética/métodosRESUMO
The polar Kerr effect in the high-T_(c) superconductor YBa2Cu3O6+x was measured at zero magnetic field with high precision using a cyogenic Sagnac fiber interferometer. We observed nonzero Kerr rotations of order approximately 1 microrad appearing near the pseudogap temperature T(*) and marking what appears to be a true phase transition. Anomalous magnetic behavior in magnetic-field training of the effect suggests that time reversal symmetry is already broken above room temperature.