3,519 research outputs found
Magnetism in tetragonal manganese-rich Heusler compounds
A comprehensive study of the total energy of manganese-rich Heusler compounds
using density functional theory is presented. Starting from a large set of
cubic parent systems, the response to tetragonal distortions is studied in
detail. We single out the systems that remain cubic from those that most likely
become tetragonal. The driving force of the tetragonal distortion and its
effect on the magnetic properties, especially where they deviate from the
Slater--Pauling rule, as well as the trends in the Curie temperatures, are
highlighted. By means of partial densities of states, the electronic structural
changes reveal the microscopic origin of the observed trends. We focus our
attention on the magnetocrystalline anisotropy and find astonishingly high
values for tetragonal Heusler compounds containing heavy transition metals
accompanied by low magnetic moments, which indicates that these materials are
promising candidates for spin-transfer torque magnetization-switching
applications
Topological insulators and thermoelectric materials
Topological insulators (TIs) are a new quantum state of matter which have
gapless surface states inside the bulk energy gap. Starting with the discovery
of two dimensional TIs, the HgTe-based quantum wells, many new topological
materials have been theoretically predicted and experimentally observed.
Currently known TI materials can possibly be classified into two families, the
HgTe family and the Bi2Se family. The signatures found in the electronic
structure of a TI also cause these materials to be excellent thermoelectric
materials. On the other hand, excellent thermoelectric materials can be also
topologically trivial. Here we present a short introduction to topological
insulators and thermoelectrics, and give examples of compound classes were both
good thermoelectric properties and topological insulators can be found.Comment: Phys. Status Solidi RRL, accepte
Lone Pair Effect, Structural Distortions and Potential for Superconductivity in Tl Perovskites
Drawing the analogy to BaBiO3, we investigate via ab-initio electronic
structure calculations potential new superconductors of the type ATlX3 with A =
Rb, Cs and X = F, Cl, and Br, with a particular emphasis on RbTlCl3. Based on
chemical reasoning, supported by the calculations, we show that Tl-based
perovskites have structural and charge instabilities driven by the lone pair
effect, similar to the case of BaBiO3, effectively becoming A2Tl1+Tl3+X6. We
find that upon hole doping of RbTlCl3, structures without Tl1+, Tl3+ charge
disproportionation become more stable, although the ideal cubic perovskite,
often viewed as the best host for superconductivity, should not be the most
stable phase in the system. The known superconductor (Sr,K)BiO3 and hole doped
RbTlCl3, predicted to be most stable in the same tetragonal structure, display
highly analogous calculated electronic band structures.Comment: 5 pages, 5 figure
Heusler 4.0: Tunable Materials
Heusler compounds are a large family of binary, ternary and quaternary
compounds that exhibit a wide range of properties of both fundamental and
potential technological interest. The extensive tunability of the Heusler
compounds through chemical substitutions and structural motifs makes the family
especially interesting. In this article we highlight recent major developments
in the field of Heusler compounds and put these in the historical context. The
evolution of the Heusler compounds can be described by four major periods of
research. In the latest period, Heusler 4.0 has led to the observation of a
variety of properties derived from topology that includes: topological metals
with Weyl and Dirac points; a variety of non-collinear spin textures including
the very recent observation of skyrmions at room temperature; and giant
anomalous Hall effects in antiferromagnetic Heuslers with triangular magnetic
structures. Here we give a comprehensive overview of these major achievements
and set research into Heusler materials within the context of recent emerging
trends in condensed matter physics
Emerging chiral edge states from the confinement of a magnetic Weyl semimetal in CoSnS
The quantum anomalous Hall effect (QAHE) and magnetic Weyl semimetals (WSMs)
are topological states induced by intrinsic magnetic moments and spin-orbit
coupling. Their similarity suggests the possibility of achieving the QAHE by
dimensional confinement of a magnetic WSM along one direction. In this study,
we investigate the emergence of the QAHE in the two-dimensional (2D) limit of
magnetic WSMs due to finite size effects in thin films and step-edges. We
demonstrate the feasibility of this approach with effective models and real
materials. To this end, we have chosen the layered magnetic WSM
CoSnS, which features a large anomalous Hall conductivity and
anomalous Hall angle in its 3D bulk, as our material candidate. In the 2D limit
of CoSnS two QAHE states exist depending on the stoichiometry of
the 2D layer. One is a semimetal with a Chern number of 6, and the other is an
insulator with a Chern number of 3. The latter has a band gap of 0.05 eV, which
is much larger than that in magnetically doped topological insulators. Our
findings naturally explain the existence of chiral states in step edges of bulk
CoSnS which habe been reported in a recent experiment at
and present a realistic avenue to realize QAH states in thin films of magnetic
WSMs.Comment: Revised 3rd version of the manuscrip
ValiTex -- a uniform validation framework for computational text-based measures of social science constructs
Guidance on how to validate computational text-based measures of social
science constructs is fragmented. Whereas scholars are generally acknowledging
the importance of validating their text-based measures, they often lack common
terminology and a unified framework to do so. This paper introduces a new
validation framework called ValiTex, designed to assist scholars to measure
social science constructs based on textual data. The framework draws on a
long-established tradition within psychometrics while extending the framework
for the purpose of computational text analysis. ValiTex consists of two
components, a conceptual model, and a dynamic checklist. Whereas the conceptual
model provides a general structure along distinct phases on how to approach
validation, the dynamic checklist defines specific validation steps and
provides guidance on which steps might be considered recommendable (i.e.,
providing relevant and necessary validation evidence) or optional (i.e., useful
for providing additional supporting validation evidence. The utility of the
framework is demonstrated by applying it to a use case of detecting sexism from
social media data
Enhancing K2 Students' Skills With Loose Parts at Kindergarten XYZ
This quasi-experimental study aims to measure the effectiveness of using loose parts as a media to enhance problem-solving, critical thinking, and creativity skills among K2 students at Kindergarten XYZ Jakarta. The research involved a control group of 26 students and an experimental group of 25 students, using pretest and posttest assessments to measure progress. The experimental group integrated loose parts into classroom activities, while the control group followed the standard curriculum. Next, the pretest and posttest data are analyzed for their n-Gain values to obtain the difference between the two groups. N-Gain is used to measure the effectiveness of an intervention or learning approach by comparing score improvements between pretest and posttest, providing an overview of the extent of improvement in the use of loose parts in the experimental group. The higher the n-Gain value, the greater the improvement achieved by that group. The results showed an increased average score in problem-solving and creativity for the experimental group compared to the control group in both pretest and posttest. However, critical thinking scores showed no significant difference between the two groups. This suggests that the use of loose parts positively impacts problem-solving and creativity in kindergarten students, but improving critical thinking may require further investigation or alternative strategies
Mixing it up: A general framework for Markovian statistics
Up to now, the nonparametric analysis of multidimensional continuous-time
Markov processes has focussed strongly on specific model choices, mostly
related to symmetry of the semigroup. While this approach allows to study the
performance of estimators for the characteristics of the process in the minimax
sense, it restricts the applicability of results to a rather constrained set of
stochastic processes and in particular hardly allows incorporating jump
structures. As a consequence, for many models of applied and theoretical
interest, no statement can be made about the robustness of typical statistical
procedures beyond the beautiful, but limited framework available in the
literature. To close this gap, we identify -mixing of the process and
heat kernel bounds on the transition density as a suitable combination to
obtain -norm and kernel invariant density estimation rates matching
the case of reversible multidimenisonal diffusion processes and outperforming
density estimation based on discrete i.i.d. or weakly dependent data. Moreover,
we demonstrate how up to -terms, optimal -norm adaptive invariant
density estimation can be achieved within our general framework based on tight
uniform moment bounds and deviation inequalities for empirical processes
associated to additive functionals of Markov processes. The underlying
assumptions are verifiable with classical tools from stability theory of
continuous time Markov processes and PDE techniques, which opens the door to
evaluate statistical performance for a vast amount of Markov models. We
highlight this point by showing how multidimensional jump SDEs with L\'evy
driven jump part under different coefficient assumptions can be seamlessly
integrated into our framework, thus establishing novel adaptive -norm
estimation rates for this class of processes
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