Observation of room temperature excitons in an atomically thin topological insulator.

Optical spectroscopy of ultimately thin materials has significantly enhanced our understanding of collective excitations in low-dimensional semiconductors. This is particularly reflected by the rich physics of excitons in atomically thin crystals which uniquely arises from the interplay of strong Coulomb correlation, spin-orbit coupling (SOC), and lattice geometry. Here we extend the field by reporting the observation of room temperature excitons in a material of non-trivial global topology. We study the fundamental optical excitation spectrum of a single layer of bismuth atoms epitaxially grown on a SiC substrate (hereafter bismuthene or Bi/SiC) which has been established as a large-gap, two-dimensional (2D) quantum spin Hall (QSH) insulator. Strongly developed optical resonances are observed to emerge around the direct gap at the K and K' points of the Brillouin zone, indicating the formation of bound excitons with considerable oscillator strength. These experimental findings are corroborated, concerning both the character of the excitonic resonances as well as their energy scale, by ab-initio GW and Bethe-Salpeter equation calculations, confirming strong Coulomb interaction effects in these optical excitations. Our observations provide evidence of excitons in a 2D QSH insulator at room temperature, with excitonic and topological physics deriving from the very same electronic structure.

Morphological and histopathological evaluation of autopsied patients with hypertensive cardiopathy.

BACKGROUND: Physiopathological processes in hypertensive heart disease are controlled by complex interactions between cardiomyocytes, extracellular matrix, microvasculature and other cells present in the myocardium. OBJECTIVE: To analyze morphological changes in hypertensive cardiopathy and to describe and compare findings in order to help clarify determinant factors. METHODS: 42 fragments of the left ventricular myocardium and circumflex branch of the left coronary artery were obtained from individuals autopsied at the Clinical Hospital of the Federal University of Triângulo Mineiro (UFTM) in the period ranging from 1984 to 2018. Groups were split into individuals with hypertensive heart disease (HD) and individuals without heart disease (ND). Wall thickness was measured with a digital caliper and Computed Tomography. Quantification of collagen fibers was conducted by computerized morphometry and mast cell density was assessed by immunohistochemical methods. RESULTS: There was a significant increase of heart weight in the HD group compared to the ND group, (p = 0.0002). There was a significant increase of thickness of the middle third of the free wall in the HD group compared to the ND group, (p = 0.04). There was a significant increase of collagen fibers in the left ventricle in the HD group compared to the ND group, (p < 0.0001). Concerning mast cell density, there was a significant increase in the left ventricle of individuals with HD immuno-labeled by the set anti-chymase/anti-tryptase (p < 0.0001). There was a significant increase of mast cell density in the circumflex branch of the left coronary artery of individuals with HD immuno-labeled by the set anti-chymase/anti-tryptase (p = 0.01). CONCLUSIONS: Mast cells are involved in the development of hypertensive heart disease, contributing to the remodeling of collagen fibers in this disease.

Signatures of Dirac fermion-mediated magnetic order.

The spin-momentum locking of topological states offers an ideal platform to explore novel magnetoelectric effects. These intimately depend on the ability to manipulate the spin texture in a controlled way. Here we combine scanning tunnelling microscopy with single-atom deposition to map the evolution of topological states under the influence of different magnetic perturbations. We obtain signatures of Dirac fermion-mediated magnetic order for extremely dilute adatom concentrations. This striking observation is found to critically depend on the single adatoms' magnetic anisotropy and the position of the Fermi level. Our findings open new perspectives in spin engineering topological states at the atomic scale and pave the way to explore novel spin-related topological phenomena with promising potential for applications.