Suchergebnisse

Scientific Highlight of the Month (March 2018). ; Single adatoms offer an exceptional playground for studying magnetism and its associated dynamics at the atomic scale. Here we review recent results on single adatoms deposited on metallic substrates, based on time-dependent density functional theory. First we analyze quantum zero-point spin-fluctuations (ZPSF) as calculated from the fluctuation-dissipation theorem, and show how they affect the magnetic stability by modifying the magnetic anisotropy energy. We also assess the impact of ZPSF in the limit of small hybridization to the substrate characteristic of semi-insulating substrates, connecting to recent experimental investigations where magnetic stability of a single adatom was achieved for the first time. Secondly, we inspect further the dynamics of single adatoms by considering the longitudinal and transverse spin-relaxation processes, whose time-scales are analyzed and related to the underlying electronic structure of both the adatom and the substrate. Thirdly, we analyze spin-fluctuation modes of paramagnetic adatoms, i.e. adatoms where the Stoner criterion for magnetism is almost fulfilled. Interestingly, such modes can develop well-defined peaks in the meV range, their main characteristics being determined by two fundamental electronic properties, namely the Stoner parameter and the density of states at the Fermi level. Furthermore, simulated inelastic scanning tunneling spectroscopy curves reveal that these spin-fluctuation modes can be triggered by tunneling electrons, opening up potential applications also for paramagnetic adatoms. Lastly, an overview of the outstanding issues and future directions is given. ; This work has been supported by the Helmholtz Gemeinschaft Deutscher-Young Investigators Group Program No. VH-NG-717 (Functional Nanoscale Structure and Probe Simulation Laboratory), the Impuls und Vernetzungsfonds der Helmholtz-Gemeinschaft Postdoc Programme, and funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (ERC-consolidator grant 681405 DYNASORE). ; Peer reviewed

We report on many-body corrections to one-electron energy spectra of bulk bismuth tellurohalides—materials that exhibit a giant Rashba-type spin splitting of the band-gap edge states.We showthat the corrections obtained in the one-shot GW approximation noticeably modify the spin-orbit-induced spin splitting evaluated within density functional theory.We demonstrate that taking into account many-body effects is crucial to interpret the available experimental data. ; We acknowledge partial support from the Basque Country Government, Departamento de Educación, Universidades e Investigación (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-00), and the Ministry of Education and Science of Russian Federation (Grant No. 2.8575.2013). ; Peer reviewed

7 pags., 4 figs., 3 pags. ; The Dzyaloshinskii-Moriya interaction (DMI) is an antisymmetric exchange interaction that stabilizes chiral spin textures. It is induced by inversion symmetry breaking in noncentrosymmetric lattices or at interfaces. Recently, interfacial DMI has been found in magnetic layers adjacent to transition metals due to the spin-orbit coupling and at interfaces with graphene due to the Rashba effect. We report direct observation of strong DMI induced by chemisorption of oxygen on a ferromagnetic layer at room temperature. The sign of this DMI and its unexpectedly large magnitude—despite the low atomic number of oxygen—are derived by examining the oxygen coverage–dependent evolution of magnetic chirality. We find that DMI at the oxygen/ ferromagnet interface is comparable to those at ferromagnet/transition metal interfaces; it has enabled direct tailoring of skyrmion's winding number at room temperature via oxygen chemisorption. This result extends the understanding of the DMI, opening up opportunities for the chemisorption-related design of spin-orbitronic devices. ; This work has been supported by the NSF (DMR-1610060 and DMR-1905468) and the UC Office of the President Multicampus Research Programs and Initiatives (MRP-17- 454963). Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under contract no. DE-AC02- 05CH11231. Work at GU has been supported, in part, by SMART (2018-NE-2861), one of seven centers of nCORE, a Semiconductor Research Corporation program, sponsored by the National Institute of Standards and Technology (NIST). A.M. and M.A.G.B. acknowledge support from MINECO (Spain) under the project no. MAT2017-87072-C4-2-P and from Comunidad de Madrid under the project no. S2018/NMT4321. The Jülich team acknowledges financial support from the DARPA TEE program through grant MIPR (# HR0011831554) from the DOI, the European Union H2020-INFRAEDI-2018-1 program (grant no. 824143, project "MaX— Materials at the exascale"), the Deutsche Forschungsgemeinschaft (DFG) through SPP 2137 "Skyrmionics" (project BL 444/16), the Collaborative Research Centers SFB 1238 (project C01), and computing resources at the supercomputers JURECA at Juelich Supercomputing Centre and JARA-HPC from RWTH Aachen University (projects jias1f and jara0197). R.L.C., A.K.S., and R.W. acknowledge financial support from the European Union via an International Marie Curie Fellowship (grant no. 748006). H.D. acknowledges the support of the National Key R&D Program of China (grant no. 2017YFA0303202) and the National Natural Science Foundation of China (grant nos. 11734006 and 51571109). E.G.M. acknowledges support from MINECO (Spain) under grants MAT2014-52477 and FIS2017-82415-R and from MECD (Spain) under grant PRX17/00557

Wannier90 is an open-source computer program for calculating maximally-localised Wannier functions (MLWFs) from a set of Bloch states. It is interfaced to many widely used electronic-structure codes thanks to its independence from the basis sets representing these Bloch states. In the past few years the development of Wannier90 has transitioned to a community-driven model; this has resulted in a number of new developments that have been recently released in Wannier90 v3.0. In this article we describe these new functionalities, that include the implementation of new features for wannierisation and disentanglement (symmetry-adapted Wannier functions, selectively-localised Wannier functions, selected columns of the density matrix) and the ability to calculate new properties (shift currents and Berry-curvature dipole, and a new interface to many-body perturbation theory); performance improvements, including parallelisation of the core code; enhancements in functionality (support for spinor-valued Wannier functions, more accurate methods to interpolate quantities in the Brillouin zone); improved usability (improved plotting routines, integration with high-throughput automation frameworks), as well as the implementation of modern software engineering practices (unit testing, continuous integration, and automatic source-code documentation). These new features, capabilities, and code development model aim to further sustain and expand the community uptake and range of applicability, that nowadays spans complex and accurate dielectric, electronic, magnetic, optical, topological and transport properties of materials. ; The WDG acknowledges financial support from the NCCR MARVEL of the Swiss National Science Foundation, the European Union's Centre of Excellence E-CAM (Grant No. 676531), and the Thomas Young Centre for Theory and Simulation of Materials (Grant No. TYC-101). ; Peer reviewed