340 research outputs found
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
Non-Fermi liquid behavior in transport through Co doped Au chains
We calculate the conductance as a function of temperature through Au
monoatomic chains containing one Co atom as a magnetic impurity, and connected
to two conducting leads with a 4-fold symmetry axis. Using the information
derived from {\it ab initio} calculations, we construct an effective model
\Heff that hybridizes a 3d quadruplet at the Co site with two 3d
triplets through the hopping of 5d and 5d electrons of Au. The
quadruplet is split by spin anisotropy due to spin-orbit coupling. Solving
\Heff with the numerical renormalization group (NRG) % Wb: reverted my own
change we find that at low temperatures and the ground
state impurity entropy is , a behavior similar to the two-channel
Kondo model. Stretching the chain leads to a non Kondo phase, with the physics
of the underscreened Kondo model at the quantum critical point.Comment: Accepted in Physical Review Letter
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
Dzyaloshinskii-Moriya interaction and Hall effects in the skyrmion phase of MnFeGe alloys
We carry out density functional theory calculations which demonstrate that
the electron dynamics in the skyrmion phase of Fe-rich MnFeGe
alloys is governed by Berry phase physics. We observe that the magnitude of the
Dzyaloshinskii-Moriya interaction, directly related to the mixed space-momentum
Berry phases, changes sign and magnitude with concentration in direct
correlation with the data of Shibata {\it et al.}, Nature Nanotech. {\bf 8},
723 (2013). The computed anomalous and topological Hall effects in FeGe are
also in good agreement with available experiments. We further develop a simple
tight-binding model able to explain these findings. Finally, we show that the
adiabatic Berry phase picture is violated in the Mn-rich limit of the alloys.Comment: 5 page
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
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
Orbital Rashba effect as a platform for robust orbital photocurrents
Orbital current has emerged over the past years as one of the key novel
concepts in magnetotransport. Here, we demonstrate that laser pulses can be
used to generate large and robust non-relativistic orbital currents in systems
where the inversion symmetry is broken by the orbital Rashba effect. By
referring to model and first principles tools, we demonstrate that orbital
Rashba effect, accompanied by crystal field splitting, can mediate robust
orbital photocurrents without a need for spin-orbit interaction even in
metallic systems. We show that such non-relativistic orbital photocurrents are
translated into derivative photocurrents of spin when relativistic effects are
taken into account. We thus promote orbital photocurrents as a promising
platform for optical generation of currents of angular momentum, and discuss
their possible applications
Laser-induced charge and spin photocurrents at BiAg surface: a first principles benchmark
Here, we report first principles calculations and analysis of laser-induced
photocurrents at the surface of a prototype Rashba system. By referring to
Keldysh non-equilibrium formalism combined with the Wannier interpolation
scheme we perform first-principles electronic structure calculations of a
prototype BiAg surface alloy, which is a well-known material realization of
the Rashba model. In addition to non-magnetic ground state situation we also
study the case of in-plane magnetized BiAg. We calculate the laser-induced
charge photocurrents for the ferromagnetic case and the laser-induced spin
photocurrents for both the non-magnetic and the ferromagnetic cases. Our
results confirm the emergence of very large in-plane photocurrents as predicted
by the Rashba model. The resulting photocurrents satisfy all the symmetry
restrictions with respect to the light helicity and the magnetization
direction. We provide microscopic insights into the symmetry and magnitude of
the computed currents based on the ab-initio multi-band electronic structure of
the system, and scrutinize the importance of resonant two-band and three-band
transitions for driven currents, thereby establishing a benchmark picture of
photocurrents at Rashba-like surfaces and interfaces. Our work contributes to
the study of the role of the interfacial Rashba spin-orbit interaction as a
mechanism for the generation of in-plane photocurrents, which are of great
interest in the field of ultrafast and terahertz spintronics
- …