420 research outputs found
Topological spin Hall effect in antiferromagnetic skyrmions
The topological Hall effect (THE), as one of the primary manifestations of
non-trivial topology of chiral skyrmions, is traditionally used to detect the
emergence of skyrmion lattices with locally ferromagnetic order. In this work
we demonstrate that the appearance of non-trivial two-dimensional chiral
textures with locally {\it anti}-ferromagnetic order can be detected through
the spin version of the THE the topological spin Hall effect (TSHE).
Utilizing the semiclassical formalism, here used to combine chiral
antiferromagnetic textures with a density functional theory description of the
collinear, degenerate electronic structure, we follow the real-space real-time
evolution of electronic SU(2) wavepackets in an external electric field to
demonstrate the emergence of sizeable transverse pure spin current in synthetic
antiferromagnets of the Fe/Cu/Fe trilayer type. We further unravel the extreme
sensitivity of the TSHE to the details of the electronic structure, suggesting
that the magnitude and sign of the TSHE in transition-metal synthetic
antiferromagnets can be engineered by tuning such parameters as the thickness
or band filling. Besides being an important step in our understanding of the
topological properties of ever more complex skyrmionic systems, our results
bear great potential in stimulating the discovery of antiferromagnetic
skyrmions
Anisotropic spin Hall effect from first principles
We report on first principles calculations of the anisotropy of the intrinsic
spin Hall conductivity (SHC) in nonmagnetic hcp metals and in antiferromagnetic
Cr. For most of the metals of this study we find large anisotropies. We derive
the general relation between the SHC vector and the direction of spin
polarization and discuss its consequences for hcp metals. Especially, it is
predicted that for systems where the SHC changes sign due to the anisotropy the
spin Hall effect may be tuned such that the spin polarization is parallel
either to the electric field or to the spin current.Comment: Accepted for publication in Physical Review Letter
Topological Crystalline Insulator and Quantum Anomalous Hall States in IV-VI based Monolayers and their Quantum Wells
Different from the two-dimensional (2D) topological insulator, the 2D
topological crystalline insulator (TCI) phase disappears when the mirror
symmetry is broken, e.g., upon placing on a substrate. Here, based on a new
family of 2D TCIs - SnTe and PbTe monolayers - we theoretically predict the
realization of the quantum anomalous Hall effect with Chern number C = 2 even
when the mirror symmetry is broken. Remarkably, we also demonstrate that the
considered materials retain their large-gap topological properties in quantum
well structures obtained by sandwiching the monolayers between NaCl layers. Our
results demonstrate that the TCIs can serve as a seed for observing robust
topologically non-trivial phases.Comment: 5 pages, submitted on 27th Feb 201
Unusual Kondo physics in a Co impurity atom embedded in noble-metal chains
We analyze the conduction bands of the one dimensional noble-metal chains
that contain a Co magnetic impurity by means of ab initio calculations. We
compare the results obtained for Cu and Ag pure chains, as well as O doped Cu,
Ag and Au chains with those previously found for Au pure chains. We find
similar results in the case of Cu and Au hosts, whereas for Ag chains a
different behavior is obtained. Differences and similarities among the
different systems are analyzed by comparing the electronic structure of the
three noble-metal hosts. The d-orbitals of Cu chains at the Fermi level have
the same symmetry as in the case of Au chains. These orbitals hybridize with
the corresponding ones of the Co impurity, giving rise to the possibility of
exhibiting a two-channel Kondo physics.Comment: Accepted in IEEE Trans. Magn. - April 201
Distinct magnetotransport and orbital fingerprints of chiral bobbers
While chiral magnetic skyrmions have been attracting significant attention in
the past years, recently, a new type of a chiral particle emerging in thin
films a chiral bobber has been theoretically predicted and
experimentally observed. Here, based on theoretical arguments, we provide a
clear pathway to utilizing chiral bobbers for the purposes of future
spintronics by uncovering that these novel chiral states possess inherent
transport fingerprints that allow for their unambiguous electrical detection in
systems comprising several types of chiral states. We reveal that unique
transport and orbital characteristics of bobbers root in the non-trivial
magnetization distribution in the vicinity of the Bloch points, and demonstrate
that tuning the details of the Bloch point topology can be used to drastically
alter the emergent response properties of chiral bobbers to external fields,
which bears great potential for engineering chiral dynamics and cognitive
computing.Comment: Supplementary available upon reques
Surface orbitronics: new twists from orbital Rashba physics
When the inversion symmetry is broken at a surface, spin-orbit interaction
gives rise to spin-dependent energy shifts - a phenomenon which is known as the
spin Rashba effect. Recently, it has been recognized that an orbital
counterpart of the spin Rashba effect - the orbital Rashba effect - can be
realized at surfaces even without spin- orbit coupling. Here, we propose a
mechanism for the orbital Rashba effect based on sp orbital hybridization,
which ultimately leads to the electric polarization of surface states. As a
proof of principle, we show from first principles that this effect leads to
chiral orbital textures in -space of the BiAg monolayer. In
predicting the magnitude of the orbital moment arising from the orbital Rashba
effect, we demonstrate the crucial role that the Berry phase theory plays for
the magnitude and variation of the orbital textures. As a result, we predict a
pronounced manifestation of various orbital effects at surfaces, and proclaim
the orbital Rashba effect to be a key platform for surface orbitronics
Crystal Hall and crystal magneto-optical effect in thin films of SrRuO
Motivated by the recently observed topological Hall effect in ultra-thin
films of SrRuO (SRO) grown on SrTiO (STO) [001] substrate, we
investigate the magnetic ground state and anomalous Hall response of the SRO
ultra-thin films by virtue of spin density functional theory (DFT). Our
findings reveal that in the monolayer limit of an SRO film, a large energy
splitting of Ru- states stabilizes an anti-ferromagnetic (AFM)
insulating magnetic ground state. For the AFM ground state, our Berry curvature
calculations predict a large anomalous Hall response upon doping. From the
systematic symmetry analysis, we uncover that the large anomalous Hall effect
arises due to a combination of broken time-reversal and crystal symmetries
caused by the arrangement of non-magnetic atoms (Sr and O) in the SRO
monolayer. We identify the emergent Hall effect as a clear manifestation of the
so-called crystal Hall effect in terminology of \v{S}mejkal et al.
arXiv:1901.00445 (2019), and demonstrate that it persists at finite frequencies
which is the manifestation of the crystal magneto-optical effect. Moreover, we
find a colossal dependence of the AHE on the degree of crystal symmetry
breaking also in ferromagnetic SRO films, which all together points to an
alternative explanation of the emergence of the topological Hall effect
observed in this type of systems.Comment: 8 pages, 5 figure
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