Ikerbasque

About: Ikerbasque is a other organization based out in Bilbao, Spain. It is known for research contribution in the topics: Graphene & Quantum. The organization has 713 authors who have published 7967 publications receiving 231990 citations. The organization is also known as: Basque Foundation for Science.

Variety of scenarios for magnetic exchange response in topological insulators

Abstract: We present an ab initio relativistic $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ theory of the effect of magnetic exchange field on the band structure in the gap region of bulk crystals and thin films of three-dimensional layered topological insulators. For the field perpendicular to the layers (along $z$), we reveal unconventional scenarios of the response of the band-gap edges to the magnetization. The modification of the valence and conduction states is considered in terms of their $\mathrm{\ensuremath{\Gamma}}$-point spin ${s}^{z}$ and total angular momentum ${J}^{z}$ on the atomic sites where the states are localized. The actual scenario depends on whether ${s}^{z}$ and ${J}^{z}$ have the same or opposite sign. In particular, the opposite sign for the valence state and the same sign for the conduction state give rise to an unconventional response in ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$---both in the bulk crystal and in ultrathin films, which fundamentally distinguishes this topological insulator from ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, where both states have the same sign. To gain a deeper insight into different scenarios in insulators with both inverted and noninverted zero-field band structure, a minimal four-band third-order $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ model is constructed from first principles. Within this model, we analyze the field-induced band structure of the insulators and identify Weyl nodes that appear in a magnetic phase and behave differently depending on the scenario. We characterize the topology of the modified band structure by the Chern number $\mathcal{C}$ and find the unconventional response to be accompanied by a large Chern number $\mathcal{C}=\ifmmode\pm\else\textpm\fi{}3$.

Expression of cellular senescence and neural stem cell markers in a case of advanced retinal fibrosis.

Abstract: Fibrosis in the posterior segment of the eye tends to be the final stage in the resolution of lesions in the retina and choroid. Two of the diseases that most often cause this type of fibrosis are diabetes and age-related macular degeneration (AMD).1 The main aetiopathogenetic mechanisms involved in the development of fibrosis are hypoxia and inflammation. In the case of AMD, retinal pigment epithelium dysfunction leads to accumulations of substances (drusen) with angiogenic activity on Bruch's membrane, this becoming thicker and limiting oxygen diffusion to the most external layers of the retina. It causes two types of lesions: dry or atrophic lesions, and wet or exudative (angiogenic) lesions.1,2 On the other hand, diabetes leads to hypoxic lesions due to microvasculopathy associated with glycosylation of the vascular wall. Both processes can lead to blindness. In AMD, cellular senescence and stem cells may play a key role in the progression of the lesions. The progressive accumulation of cell damage over time promotes the induction of senescence in which cells block their capacity to divide and acquire functions for biosynthesis and secretion of various different cytokines (senescence-associated secretory phenotype), which in turn leads to immunological and remodelling responses of the extracellular matrix, associated with repair mechanisms in damaged tissues.1-3 The inflammatory damage may, however, remain and increase, despite a reparatory inflammatory response. With age there is stem cell deficiency and hence an inability to regenerate the damaged structures.4 The progressive accumulation of senescent cells and stem cell depletion with aging may be the basis of the deterioration of the mechanisms of tissue homeostasis activated in response to damage and, consequently, responsible for fibrosis accumulation.

Chiral asymmetry detected in a 2D array of permalloy square nanomagnets using circularly polarized X ray Resonant Magnetic Scattering

Abstract: The sensitivity of Circularly polarized X ray Resonant Magnetic Scattering (CXRMS) to chiral asymmetry has been demonstrated. The study was performed on a 2D array of Permalloy (Py) square nanomagnets of 700 nm lateral size arranged in a chess lattice of 1000 nm lattice parameter. Previous X ray Magnetic Circular Dichroism Photoemission Electron microscopy (XMCD-PEEM) images on this sample showed the formation of vortices at remanence and a preference in their chiral state. The magnetic hysteresis loops of the array along the diagonal axis of the squares indicate a non-negligible and anisotropic interaction between vortices. The intensity of the magnetic scattering using circularly polarized light along one of the diagonal axes of the square magnets becomes asymmetric in intensity in the direction transversal to the incident plane at fields where the vortex states are formed. The asymmetry sign is inverted when the direction of the applied magnetic field is inverted. The result is the expected in the presence of an unbalanced chiral distribution. The effect is observed by CXRMS due to the interference between the charge scattering and the magnetic scattering.

Crystal Structures and Phase Transitions of Sr2CrSbO6.

Abstract: Sr2CrSbO6 was synthesized by the conventional solid-state reaction process. X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) has been used to reinvestigate the structure at room temperature and to study the phase transitions at high- and low-temperature. Rietveld analysis revealed that Sr2CrSbO6 crystallizes at room temperature in a monoclinic system having a space group I2/m, with a=5.5574(1) A; b=5.5782(1) A; c=7.8506(2) A and β=90.06(2), no P21/n space group as was previously reported. The high-temperature study (300–870 K) has shown that the compound presents the following temperature induced phase-transition sequence: I2/m–I4/m–Fm-3m. The low-temperature study (100–300 K) demonstrated that the room-temperature I2/m monoclinic symmetry seems to be stable down to 100 K.

Front Cover: Gas‐Phase Errors Affect DFT‐Based Electrocatalysis Models of Oxygen Reduction to Hydrogen Peroxide (ChemElectroChem 11/2022)

Abstract: The Front Cover shows that there are three ways of simulating the energy landscape of oxygen reduction to hydrogen peroxide with density functional theory: without any corrections (yellow), with O2 corrections (yellow/red), and with O2 and H2O2 corrections (red); only the latter agrees with experiments. More information can be found in the Research Article by M. O. Almeida et al.