Topological magnons driven by the Dzyaloshinskii-Moriya interaction in the centrosymmetric ferromagnet Mn5_5Ge3_3

The phase of the quantum-mechanical wave function can encode a topological structure with wide-ranging physical consequences, such as anomalous transport effects and the existence of edge states robust against perturbations. While this has been exhaustively demonstrated for electrons, properties associated with the elementary quasiparticles in magnetic materials are still underexplored. Here, we show theoretically and via inelastic neutron scattering experiments that the bulk ferromagnet Mn$_5$Ge$_3$ hosts gapped topological Dirac magnons. Although inversion symmetry prohibits a net Dzyaloshinskii-Moriya interaction in the unit cell, it is locally allowed and is responsible for the gap opening in the magnon spectrum. This gap is predicted and experimentally verified to close by rotating the magnetization away from the $c$-axis with an applied magnetic field. Hence, Mn$_5$Ge$_3$ realizes a gapped Dirac magnon material in three dimensions. Its tunability by chemical doping or by thin film nanostructuring defines an exciting new platform to explore and design topological magnons. More generally, our experimental route to verify and control the topological character of the magnons is applicable to bulk centrosymmetric hexagonal materials, which calls for systematic investigation.Comment: 24 pages, 4 figures. Accepted in Nature Communication

Pulse-height-spectrum distortion in xenon gaseous detectors for soft X-rays: experimental results

The results of an experimental determination of the pulse-height distortion in soft X-ray spectra in gaseous xenon detectors are presented. The study confirms previous Monte Carlo simulation results and emphasizes the importance of the electric field in the drift region in reducing spectral degradation while the effect of a strong magnetic field in the same region is shown to be negligibleJNICT (Junta Nacional de Investigação Científica e Tecnológica) Projecto STRDA/P/CEN/422/9

An overview of the spin dynamics of antiferromagnetic Mn5_5Si3_3

The metallic compound Mn$_5$Si$_3$ hosts a series of antiferromagnetic phases which can be controlled by external stimuli such as temperature and magnetic field. In this work, we investigate the spin-excitation spectrum of bulk Mn$_5$Si$_3$ by combining inelastic neutron scattering measurements and density functional theory calculations. We study the evolution of the dynamical response under external parameters and demonstrate that the spin dynamics of each phase is robust against any combination of temperature and magnetic field. In particular, the high-energy spin dynamics is very characteristic of the different phases consisting of either spin waves or broad fluctuations patterns.Comment: 5 figure

Análise morfológica de acessos de mandioca identificados como duplicatas de acessos com base em marcadores moleculares.

A mandioca (Manihot esculenta Crantz) apresenta ampla variabilidade genética decorrente da polinização cruzada e da alta heterozigosidade da espécie. A pesquisa com recursos genéticos desta espécie é o ponto de partida para viabilizar a pesquisa com recursos genéticos, visando o correto manejo do germoplasma e a formação de uma base de dados que garanta informação consistente ao melhorista

Recursos genéticos de Passiflora edulis Sims: caracterização e perspectivas de uso.

O maracujazeiro amarelo, pertencente à espécie Passiflora edulis Sims. é nativo do Brasil, e por isso o país possui a máxima variabilidade da espécie. Contudo, os trabalhos de melhoramento têm focado na exploração de poucos genótipos, muitas vezes pelo desconhecimento da variabilidade disponível para características de maior interesse agronômico. De fato, isso acontece em função das poucas informações sistematizadas a respeito dos acessos de germoplasma de maracujazeiro amarelo

Zigzag graphene nanoribbon edge reconstruction with stone-wales defects

In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon.Fundacao para a Ciência e a Tecnologia (FCT) SFRH/BD/44456/2008.FEDER - Programa Operacional Factores de Competitividade - COMPET