100 research outputs found
Spectroscopic perspective on the interplay between electronic and magnetic properties of magnetically doped topological insulators
We combine low energy muon spin rotation (LE-SR) and soft-X-ray
angle-resolved photoemission spectroscopy (SX-ARPES) to study the magnetic and
electronic properties of magnetically doped topological insulators,
(Bi,Sb)Te. We find that one achieves a full magnetic volume fraction in
samples of (V/Cr)(Bi,Sb)Te at doping levels x 0.16.
The observed magnetic transition is not sharp in temperature indicating a
gradual magnetic ordering. We find that the evolution of magnetic ordering is
consistent with formation of ferromagnetic islands which increase in number
and/or volume with decreasing temperature. Resonant ARPES at the V edge
reveals a nondispersing impurity band close to the Fermi level as well as V
weight integrated into the host band structure. Calculations within the
coherent potential approximation of the V contribution to the spectral function
confirm that this impurity band is caused by V in substitutional sites. The
implications of our results on the observation of the quantum anomalous Hall
effect at mK temperatures are discussed
Proximity-Induced Odd-Frequency Superconductivity in a Topological Insulator
At an interface between a topological insulator (TI) and a conventional
superconductor (SC), superconductivity has been predicted to change
dramatically and exhibit novel correlations. In particular, the induced
superconductivity by an -wave SC in a TI can develop an order parameter with
a -wave component. Here we present experimental evidence for an unexpected
proximity-induced novel superconducting state in a thin layer of the
prototypical TI, BiSe, proximity coupled to Nb. From depth-resolved
magnetic field measurements below the superconducting transition temperature of
Nb, we observe a local enhancement of the magnetic field in BiSe that
exceeds the externally applied field, thus supporting the existence of an
intrinsic paramagnetic Meissner effect arising from an odd-frequency
superconducting state. Our experimental results are complemented by theoretical
calculations supporting the appearance of such a component at the interface
which extends into the TI. This state is topologically distinct from the
conventional Bardeen-Cooper-Schrieffer state it originates from. To the best of
our knowledge, these findings present a first observation of bulk odd-frequency
superconductivity in a TI. We thus reaffirm the potential of the TI-SC
interface as a versatile platform to produce novel superconducting states.Comment: Accepted version for publication in Physical Review Letter
Collective topological spin dynamics in a correlated spin glass
The interplay between spin-orbit interaction (SOI) and magnetic order is
currently one of the most active research fields in condensed matter physics
and leading the search for materials with novel and tunable magnetic and spin
properties. Here we report on a variety of unexpected and unique observations
in thin multiferroic \GeMnTe films. The ferrimagnetic order in this
ferroelectric semiconductor is found to reverse with current pulses six orders
of magnitude lower as for typical spin-orbit torque systems. Upon a switching
event, the magnetic order spreads coherently and collectively over macroscopic
distances through a correlated spin-glass state. Lastly, we present a novel
methodology to controllably harness this stochastic magnetization dynamics,
allowing us to detect spatiotemporal nucleation of topological spin textures we
term ``skyrmiverres''.Comment: 26 pages, 10 figures, 2 table
Weyl-fermions, Fermi-arcs, and minority-spin carriers in ferromagnetic CoS2
The pyrite compound CoS2 has been intensively studied in the past due to its
itinerant ferromagnetism and potential for half-metallicity, which make it a
promising material for spintronic applications. However, its electronic
structure remains only poorly understood. Here we use complementary bulk- and
surface-sensitive angle-resolved photoelectron spectroscopy and ab-initio
calculations to provide a complete picture of its band structure. We discover
Weyl-cones at the Fermi-level, which presents CoS2 in a new light as a rare
member of the recently discovered class of magnetic topological metals. We
directly observe the topological Fermi-arc surface states that link the
Weyl-nodes, which will influence the performance of CoS2 as a spin-injector by
modifying its spin-polarization at interfaces. Additionally, we are for the
first time able to directly observe a minority-spin bulk electron pocket in the
corner of the Brillouin zone, which proves that CoS2 cannot be a true
half-metal. Beyond settling the longstanding debate about half-metallicity in
CoS2, our results provide a prime example of how the topology of magnetic
materials can affect their use in spintronic applications
Controllable orbital angular momentum monopoles in chiral topological semimetals
The emerging field of orbitronics aims at generating and controlling currents
of electronic orbital angular momentum (OAM) for information processing.
Structurally chiral topological crystals could be particularly suitable
orbitronic materials because they have been predicted to host topological band
degeneracies in reciprocal space that are monopoles of OAM. Around such a
monopole, the OAM is locked isotopically parallel or antiparallel to the
direction of the electron's momentum, which could be used to generate large and
controllable OAM currents. However, OAM monopoles have not yet been directly
observed in chiral crystals, and no handle to control their polarity has been
discovered. Here, we use circular dichroism in angle-resolved photoelectron
spectroscopy (CD-ARPES) to image OAM monopoles in the chiral topological
semimetals PtGa and PdGa. Moreover, we also demonstrate that the polarity of
the monopole can be controlled via the structural handedness of the host
crystal by imaging OAM monopoles and anti-monopoles in the two enantiomers of
PdGa, respectively. For most photon energies used in our study, we observe a
sign change in the CD-ARPES spectrum when comparing positive and negative
momenta along the light direction near the topological degeneracy. This is
consistent with the conventional view that CD-ARPES measures the projection of
the OAM monopole along the photon momentum. For some photon energies, however,
this sign change disappears, which can be understood from our numerical
simulations as the interference of polar atomic OAM contributions, consistent
with the presence of OAM monopoles. Our results highlight the potential of
chiral crystals for orbitronic device applications, and our methodology could
enable the discovery of even more complicated nodal OAM textures that could be
exploited for orbitronics.Comment: 16 pages, 8 figure
Putative Chemosensory Receptors of the Codling Moth, Cydia pomonella, Identified by Antennal Transcriptome Analysis
The codling moth, Cydia pomonella, is an important fruit pest worldwide. As nocturnal animals, adults depend to a large extent on olfactory cues for detection of food and mates, and, for females, oviposition sites. In insects, odor detection is mediated by odorant receptors (ORs) and ionotropic receptors (IRs), which ensure the specificity of the olfactory sensory neuron responses. In this study, our aim was to identify chemosensory receptors in the codling moth as a means to uncover new targets for behavioral interference. Using next-generation sequencing techniques, we identified a total of 43 candidate ORs, one gustatory receptor and 15 IRs in the antennal transcriptome. Through Blast and sequence similarity analyses we annotated the insect obligatory co-receptor ORco, five genes clustering in a conserved clade containing sex pheromone receptors, one homolog of the Bombyx mori female-enriched receptor BmorOR30 (but no homologs of the other B. mori female-enriched receptors) and one gene clustering in the sugar receptor family. Among the candidate IRs, we identified homologs of the two highly conserved co-receptors IR8a and IR25a, and one homolog of an IR involved in phenylethyl amine detection in Drosophila. Our results open for functional characterization of the chemosensory receptors of C. pomonella, with potential for new or refined applications of semiochemicals for control of this pest insect
Design principles in housing for people with complex physical and cognitive disability: towards an integrated framework for practice
To develop a research-based environmental framework to guide the design and construction of suitable residential dwellings for individuals with complex disability. An environmental approach to housing design and development recognises that there are physical, psychological and social components relating to housing design, dwelling location and the neighbourhood context, and that these elements interact to affect the physical, psychological, and social wellness of individuals. Following theoretical review and synthesis, a comprehensive set of design features that are conducive to residents’ wellness and quality of life are described. It is clear that housing design and development for people with complex disability ought to consider the physical, social, natural, symbolic, and care environment in relation to housing design, dwelling location, and the neighbourhood context for improved housing outcomes. An integrated housing design and development framework is presented. It is hoped this practical matrix/evaluative tool will inform future inclusive housing design and development decisions in Australia and internationally. The application of this framework is especially relevant to political climates striving to achieve design innovation to increase housing choice for people with complex disability
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