pinecone/core-2020-05-10-deduplication huggingface dataset:
Dzyaloshinskii-Moriya interactions and magnetic texture in the Fe films
  deposited on transition-metal dichalcogenides

The magnetic properties of materials based on two-dimensional
transition-metal dichalcogenides (TMDC) have been investigated by means of
first-principles DFT calculations, namely Fe-intercalated bulk
Fe$_{1/4}$TaS$_2$ compounds as well as TMDC monolayers with deposited Fe films.
Changing the structure and the composition of systems consisting of Fe
overlayers on top of a TMDC monolayers resulted in considerable variations of
their physical properties. For the considered systems the Dzyaloshinskii-Moriya
(DM) interaction has been determined and used for the subsequent investigation
of their magnetic structure using Monte Carlo simulations. Rather strong DM
interactions as well as large $D/J$ ratios have been obtained in some of these
materials, which can lead to the formation of skyrmionic structures varying
with the strength of the applied external magnetic field
Theory of optical properties of graphene quantum dots

We present here a theory of the optical properties of graphene quantum dots (GQDs) with tunable band gaps by lateral size confinement, from UV to THz. Starting from the Hartree-Fock ground state, we construct the correlated many-body ground and excited states of GQDs as a linear combination of a finite number of electron-hole pair excitations. We discuss the evolution of the band gap with size and its renormalization by self-energy and excitonic effects. We calculate and analyze the dipole moments of graphene quantum dots that possess a degenerate valence and conduction band edge, and construct a characteristic exciton and biexciton spectrum. We find an exciton band consisting of a pair of robust, spin singlet bright exciton states and a band of dark, spin singlet and spin triplet, exciton states at lower energies. We predict a characteristic band of biexciton levels at the band edge, discuss the Auger processes and identify a biexciton-exciton cascade. Our theoretical results are compared with experimental linear absorption and non-linear transient absorption spectra of colloidal GQDs. We next discuss the optical properties of triangular GQDs with zigzag edges whose magnetic moment can be controlled by gates. The control over the magnetic moment through carrier density manipulation results in optical spin blockade and gate tunable optical properties over a wide range of photon energies.The Science Academy, Turkey, under the BAGEP program; TUBITAK, under the BIDEP progra
Observation of anisotropic interlayer Raman modes in few-layer ReS2

ReS$_2$ has recently emerged as a new member in the rapidly growing family of
two-dimensional materials. Unlike MoS$_2$ or WSe$_2$, the optical and
electrical properties of ReS$_2$ are not isotropic due to the reduced symmetry
of the crystal. Here, we present layer-dependent Raman measurements of ReS$_2$
samples ranging from monolayers to ten layers in the ultralow frequency regime.
We observe layer breathing and shear modes which allow for easy assignment of
the number of layers. Polarization-dependent measurements give further insight
into the crystal structure and reveal an energetic shift of the shear mode
which stems from the in-plane anisotropy of the shear modulus in this material
Interplay of spin-orbit coupling and superconducting correlations in germanium telluride thin films

There is much current interest in combining superconductivity and spin-orbit coupling in order to induce the topological superconducting phase and associated Majorana-like quasiparticles which hold great promise towards fault-tolerant quantum computing. Experimentally these effects have been combined by the proximity-coupling of superconducting leads and high spin-orbit materials such as InSb and InAs, or by controlled Cu-doping of topological insulators such as Bi2Se3. However, for practical purposes, a single-phase material which intrinsically displays both these effects is highly desirable. Here we demonstrate coexisting superconducting correlations and spin-orbit coupling in molecular-beam-epitaxy-grown thin films of GeTe. The former is evidenced by a precipitous low-temperature drop in the electrical resistivity which is quelled by a magnetic field, and the latter manifests as a weak antilocalisation (WAL) cusp in the magnetotransport. Our studies reveal several other intriguing features such as the presence of two-dimensional rather than bulk transport channels below 2 K, possible signatures of topological SC, and unexpected hysteresis in the magnetotransport. Our work demonstrates GeTe to be a potential host of topological SC and Majorana-like excitations, and to be a versatile platform to develop quantum information device architectures.V.N., T.-A.N and R.M. acknowledge funding from EPSRC (UK) and the Leverhulme Trust, UK. G.M. acknowledges financial support from the DFG-funded priority programme SPP1666. VN acknowledges useful discussions with Niladri Banerjee, David English, and Edmund Owen.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/pssr.20151043
Topological nature of in-gap bound states in disordered large-gap
  monolayer transition metal dichalcogenides

We propose a physical model based on disordered (a hole punched inside a
material) monolayer transition metal dichalcogenides (TMDs) to demonstrate a
large-gap quantum valley Hall insulator. We find an emergence of bound states
lying inside the bulk gap of the TMDs. They are strongly affected by
spin-valley coupling, rest- and kinetic- mass terms and the hole size. In
addition, in the whole range of the hole size, at least two in-gap bound states
with opposite angular momentum, circulating around the edge of the hole, exist.
Their topological insulator (TI) feature is analyzed by the Chern number,
characterized by spacial distribution of their probabilities and confirmed by
energy dispersion curves (Energy vs. angular momentum). It not only sheds light
on overcoming low-temperature operating limitation of existing narrow-gap TIs,
but also opens an opportunity to realize valley- and spin- qubits.Comment: 5 pages, 5 figures. Feedback is welcome
Superconductivity of Ta34Nb33Hf8Zr14Ti11 high entropy alloy from first
  principles calculations

The Korringa-Kohn-Rostoker method with the coherent potental approximation
(KKR-CPA) is applied to study the first superconducting high entropy alloy
(HEA) Ta34Nb33Hf8Zr14Ti11 (discovered in 2014 with Tc = 7.3 K), focusing on
estimations of the electron-phonon coupling constant \lambda. Electronic part
of \lambda has been calculated using the rigid muffin-tin approximation (RMTA),
while the phonon part has been approximated using average atomic mass and
experimental Debye temperature. The estimated \lambda = 1.16 is close to the
value determined from specific heat measurements, \lambda = 0.98, and suggests
rather strong electron-phonon coupling in this material.Comment: 5 pages, 4 figures, to be published in Physica Status Solidi Rapid
  Research Letter
Demonstration of polycrystalline thin film coatings on glass for spin Seebeck energy harvesting

This is an Open Access Article. It is published by Wiley under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/The spin Seebeck effect, a newly discovered phenomena, has been suggested as a potential ‘game changer’ for thermoelectric\ud
technology due to the possibility of separating the electric and thermal conductivities. This is due to a completely different device architecture where, instead of an arrangement of p- and n-type pillars between two ceramic blocks, a thermopile\ud
could be deposited directly onto a magnetic film of interest. Here we report on the spin Seebeck effect in polycrystalline Fe3O4 :Pt bilayers deposited onto amorphous glass substrates with a view for economically viable energy harvesting. Crucially, these films exhibit large coercive fields (197 Oe)\ud
and retain 75% of saturation magnetisation, in conjunction with energy conversion comparable to epitaxially grown films. This demonstrates the potential of this technology for widespread application in harvesting waste heat for electricity
Ag fractals formed on top of a porous TiO2 thin film

This work demonstrates the formation of Ag fractals on top of a Ag:TiO2 thin film. The 
dendrite-type objects emerged from a homogeneous and highly transparent Ag:TiO2 
nanocomposite, via the mechanism of diffusion-limited-aggregation of Ag atoms, 
during heat-treatment at 500 ºC. A porous TiO2 matrix was also formed during this 
process, opening a wide range of possible applications, namely in sensing-based ones, 
together with surface enhanced spectroscopies. Furthermore, fractals incorporate a wide 
range of shapes and spatial scales, inducing a potentially interesting optical response, 
over the whole visible range, presumably related with localized surface plasmon modes 
with very broad spectral distribution.This research was sponsored by FEDER funds through the COMPETE program 
(Programa Operacional Factores de Competitividade) and by FCT (Fundação para a 
Ciência e a Tecnologia), under the projects UID/FIS/04650/2013 and 
PEstOE/MAT/UI0013/2014. A. Ferreira and C. Lopes acknowledge also FCT for grants 
SFRH/BPD/102402/2014 and SFRH/BD/103373/2014
First-principles identification of defect levels in Er-doped GaN

Erbium (Er) doped GaN has been studied extensively for optoelectronic
applications, yet its defect physics is still not well understood. In this
work, we report a first-principles hybrid density functional study of the
structure, energetics, and thermodynamic transition levels of Er-related defect
complexes in GaN. We discover for the first time that Er$_{\rm Ga}$-C$_{\rm
N}$-$V_{\rm N}$, a defect complex of Er, a C impurity, and an N vacancy, and
Er$_{\rm Ga}$-O$_{\rm N}$-$V_{\rm N}$, a complex of Er, an O impurity, and an N
vacancy, form defect levels at 0.18 and 0.46 eV below the conduction band,
respectively. Together with Er$_{\rm Ga}$-$V_{\rm N}$, a defect complex of Er
and an N vacancy which has recently been found to produce a donor level at 0.61
eV, these defect complexes provide explanation for the Er-related defect levels
observed in experiments. The role of these defects in optical excitation of the
luminescent Er center is also discussed.Comment: 4 pages, 3 figure
Block antiferromagnetism and possible ferroelectricity in KFe$_2$Se$_2$

Superconductors and multiferroics are two of the hottest branches in
condensed matter physics. The connections between those two fields are
fundamentally meaningful to unify the physical rules of correlated electrons.
Recently, BaFe$_2$Se$_3$, was predicted to be multiferroic [Phys. Rev. Lett.
113, 187204 (2014)] due to its unique one-dimensional block-type
antiferromagnetism. Here, another iron-selenide KFe$_2$Se$_2$, a parent state
of iron-based superconductor, is predicted to be multiferroic. Its
two-dimensional block-type antiferromagnetism can generate a moderate electric
dipole for each Fe-Se layer via the Fe-Se-Fe exchange striction. Different
stacking configurations of these magnetic blocks give closely proximate
energies and thus the ground state of KFe$_2$Se$_2$ may be switchable between
antiferroelectric and ferroelectric phases.Comment: 5 pages, 4 figure
Potential-inserted quantum well design for quantum cascade terahertz
  lasers

We report on a new design of terahertz quantum cascade laser based on a
single, potential-inserted quantum well active region. The quantum well
properties are engineered through single monolayer InAs inserts. The modeling
is based on atomistic, spds* tight-binding calculations, and performances are
compared to that of the classical three-well design. We obtain a 100% increase
of the oscillator strength per unit length, while maintaining a high, nearly
temperature-independent contrast between phonon-induced relaxation times of the
upper and lower lasing states. The improved performances are expected to allow
THz lasing at room temperature
Field-free, spin-current control of magnetization in non-collinear
  chiral antiferromagnets

Non-collinear chiral antiferromagnets like Mn3Sn and Mn3Ge are known to show
gigantic anomalous Hall response depending on the orientation of their inverse
chiral magnetic order of Mn atoms in Kagome layers. Here we study the stability
of such magnetic order in the absence of external magnetic fields on the basis
of stochastic Landau-Lifshitz-Gilbert equation for a simplified two-dimensional
model of these materials. We find that even without external magnetic fields,
the ordered state is, once formed, highly stable against thermal fluctuations.
Moreover, we show that if Mn spins are well confined inside each Kagome layers,
by injecting spin-current using spin-filtering effect of ferromagnetic metals,
we can control the in-plane magnetic structure in a field free way.Comment: 5 pages, 4 figure
Spin Hall magnetoresistance in antiferromagnet/normal metal bilayers

We predict the emergence of spin Hall magnetoresistance in a magnetic bilayer
composed of a normal metal adjacent to an antiferromagnet. Based on a recently
derived drift-diffusion equation, we show that the resistance of the bilayer
depends on the relative angle between the direction transverse to the current
flow and the N\'eel order parameter. Although this effect presents striking
similarities with the spin Hall magnetoresistance recently reported in
ferromagnetic bilayers, in the present case its physical origin is attributed
to the anisotropic spin relaxation of itinerant spins in the antiferromagnet.Comment: 5 pages, 3 figure
Co-sputtered PtMnSb thin films and PtMnSb/Pt bilayers for spin-orbit
  torque investigations

The manipulation of the magnetization by spin-orbit torques (SOTs) has
recently been extensively studied due to its potential for efficiently writing
information in magnetic memories. Particular attention is paid to
non-centrosymmetric systems with space inversion asymmetry, where SOTs emerge
even in single-layer materials. The half-metallic half-Heusler PtMnSb is an
interesting candidate for studies of this intrinsic SOT. Here, we report on the
growth and epitaxial properties of PtMnSb thin films and PtMnSb/Pt bilayers
deposited on MgO(001) substrates by dc magnetron co-sputtering at high
temperature in ultra-high vacuum. The film properties were investigated by
x-ray diffraction, x-ray reflectivity, atomic force microscopy, and electron
microscopy. Thin PtMnSb films present a monocrystalline C1b phase with (001)
orientation, coexisting at increasing thickness with a polycrystalline phase
with (111) texture. Films thinner than about 5 nm grow in islands, whereas
thicker films grow layer-by-layer, forming a perfect MgO/PtMnSb interface. The
thin PtMnSb/Pt bilayers also show island growth and a defective transition
zone, while thicker films grow layer-by-layer and Pt grows epitaxially on the
half-Heusler compound without significant interdiffusion.Comment: 5 pages, 4 figure
Phase discrimination in CdSe structures by means of Raman scattering

Raman spectra of epitaxial layers of CdSe grown by molecular beam epitaxy have been measured for the cubic (zincblende) and hexagonal (wurtzite) phases. The Raman spectra are examined in the light of density functional calculations for these two highly similar structures. Characteristic Raman frequencies and spectral features associated with the different symmetry are discussed and reliable criteria for phase discrimination based on Raman spectroscopy are proposed. Although LO frequencies are virtually identical in both structures and may be affected by size effects, the observation of a low energy E2 mode at 33cm-1 unambiguously identifies the wurtzite structure and can be used as a specific fingerprint to distinguish between these two phases in CdSe-based nanostructures. The slightly lower LO frequency measured in the zincblende epitaxial layer is ascribed to residual tensile strain. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This work has been supported by the Spanish MINECO under contract no. MAT2015-71035-R.Peer reviewe
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
Concepts of antiferromagnetic spintronics

Antiferromagnetic spintronics is an emerging research field whose focus is on
the electrical and optical control of the antiferromagnetic order parameter and
its utility in information technology devices. An example of recently
discovered new concepts is the N\'{e}el spin-orbit torque which allows for the
antiferromagnetic order parameter to be controlled by an electrical current in
common microelectronic circuits. In this review we discuss the utility of
antiferromagnets as active and supporting materials for spintronics, the
interplay of antiferromagnetic spintronics with other modern research fields in
condensed matter physics, and its utility in future "More than Moore"
information technologies.Comment: Overview of the topics presented at the Workshop of Antiferromagnetic
  Spintronics, 2016, Mainz, German
Route Towards Dirac and Weyl Antiferromagnetic Spintronics

Topological quantum matter and spintronics research have been developed to a
large extent independently. In this Review we discuss a new role that the
antiferromagnetic order has taken in combining topological matter and
spintronics. This occurs due to the complex microscopic symmetries present in
antiferromagnets that allow, e.g., for topological relativistic quasiparticles
and the newly discovered N\'{e}el spin-orbit torques to coexist. We first
introduce the concepts of topological semimetals and spin-orbitronics.
Secondly, we explain the antiferromagnetic symmetries on a minimal Dirac
semimetal model and the guiding role of $\textit{ab initio}$ calculations in
predictions of examples of Dirac, and Weyl antiferromagnets:
SrMnBi$_{\text{2}}$, CuMnAs, and Mn$_{\text{3}}$Ge. Lastly, we illustrate the
interplay of Dirac quasiparticles, topology and antiferromagnetism on: (i) the
experimentally observed quantum Hall effect in EuMnBi$_{\text{2}}$, (ii) the
large anomalous Hall effect in Mn$_{\text{3}}$Ge, and (iii) the theoretically
predicted topological metal-insulator transition in CuMnAs.Comment: 17 pages, 11 figures, revie
Migration of Mg and other interstitial metal dopants in GaN

The minimum energy paths for the migration of interstitial Mg in wurtzite GaN
are studied through density functional calculations. The study also comprises
Li, Na, and Be dopants to examine the dependence on size and charge of the
dopant species. In all cases considered, the impurities diffuse like ions
without any tendency of localizing charge. Li, Mg, and to some extent Na,
diffuse almost isotropically in GaN, with average diffusion barriers of 1.1,
2.1, and 2.5 eV, respectively. Instead Be shows a marked anisotropy with energy
barriers of 0.76 and 1.88 eV for diffusion paths perpendicular and parallel to
the c-axis. The diffusion barrier generally increases with ionic charge and
ionic radius, but their interplay is not trivial. The calculated migration
barrier for Mg is consistent with the values estimated in a recent beta-
emission channeling experiment
Cleaning graphene: comparing heat treatments in air and in vacuum

Surface impurities and contamination often seriously degrade the properties
of two-dimensional materials such as graphene. To remove contamination, thermal
annealing is commonly used. We present a comparative analysis of annealing
treatments in air and in vacuum, both ex situ and "pre-situ", where an
ultra-high vacuum treatment chamber is directly connected to an
aberration-corrected scanning transmission electron microscope. While ex situ
treatments do remove contamination, it is challenging to obtain atomically
clean surfaces after ambient transfer. However, pre-situ cleaning with
radiative or laser heating appears reliable and well suited to clean graphene
without undue damage to its structure.Comment: 5 pages, 4 figure
Valley Dynamics of Excitons in Monolayer Dichalcogenides

Monolayer transition-metal dichalcogenides (TMDCs) have recently emerged as
possible candidates for valleytronic applications, as the spin and valley
pseudospin are directly coupled and stabilized by a large spin splitting. In
these semiconducting materials, optically excited electron-hole pairs form
tightly Coulomb-bound excitons with large binding energies. The selection rules
for excitonic transitions allow for direct optical generation of a
valley-polarized exciton population using resonant excitation. Here, we
investigate the exciton valley dynamics in monolayers of three different TMDCs
by means of time-resolved Kerr rotation at low temperatures. We observe
pronounced differences in the valley dynamics of tungsten- and molybdenum-based
TMDCs, which are directly related to the opposite order of the conduction-band
spin splitting in these materials
Dry transfer of CVD graphene using MoS$_2$-based stamps

Recently, a contamination-free dry transfer method for graphene grown by
chemical vapor deposition (CVD) has been reported that allows to directly
pick-up graphene from the copper growth substrate using a flake of hexagonal
boron nitride (hBN), resulting in ultrahigh charge carrier mobility and low
overall doping. Here, we report that not only hBN, but also flakes of
molybdenum disulfide (MoS$_2$) can be used to dry transfer graphene. This, on
one hand, allows for the fabrication of complex van-der-Waals heterostructures
using CVD graphene combined with different two-dimensional materials and, on
the other hand, can be a route towards a scalable dry transfer of CVD graphene.
The resulting heterostructures are studied using low temperature transport
measurements revealing a strong charge carrier density dependence of the
carrier mobilities (up to values of 12,000 cm$^2$/(Vs)) and the residual charge
carrier density fluctuations near the charge neutrality point when changing the
carrier density in the MoS$_2$ by applying a top gate voltage.Comment: 5 pages, 3 figure