Discovery of magnetic Weyl fermions: Dirac fermions split into pairs of Weyl fermions by slow magnetic fluctuations.
Weyl fermions as emergent quasiparticles can arise in Weyl semimetals (WSMs) in ...which the energy bands are nondegenerate, resulting from inversion or time-reversal symmetry breaking. Nevertheless, experimental evidence for magnetically induced WSMs is scarce. Here, using photoemission spectroscopy, we observe that the degeneracy of Bloch bands is already lifted in the paramagnetic phase of EuCd
2
As
2
. We attribute this effect to the itinerant electrons experiencing quasi-static and quasi–long-range ferromagnetic fluctuations. Moreover, the spin-nondegenerate band structure harbors a pair of ideal Weyl nodes near the Fermi level. Hence, we show that long-range magnetic order and the spontaneous breaking of time-reversal symmetry are not essential requirements for WSM states in centrosymmetric systems and that WSM states can emerge in a wider range of condensed matter systems than previously thought.
Abstract
Constrained by the Nielsen-Ninomiya no-go theorem, in all so-far experimentally determined Weyl semimetals (WSMs) the Weyl points (WPs) always appear in pairs in the momentum space with no ...exception. As a consequence, Fermi arcs occur on surfaces which connect the projections of the WPs with opposite chiral charges. However, this situation can be circumvented in the case of unpaired WP, without relevant surface Fermi arc connecting its surface projection, appearing singularly, while its Berry curvature field is absorbed by nontrivial charged nodal walls. Here, combining angle-resolved photoemission spectroscopy with density functional theory calculations, we show experimentally that a singular Weyl point emerges in PtGa at the center of the Brillouin zone (BZ), which is surrounded by closed Weyl nodal walls located at the BZ boundaries and there is no Fermi arc connecting its surface projection. Our results reveal that nontrivial band crossings of different dimensionalities can emerge concomitantly in condensed matter, while their coexistence ensures the net topological charge of different dimensional topological objects to be zero. Our observation extends the applicable range of the original Nielsen-Ninomiya no-go theorem which was derived from zero dimensional paired WPs with opposite chirality.
School‐aged children with autism spectrum disorders (ASDs) have delayed gestural development, in comparison with age‐matched typically developing children. In this study, an intervention program ...taught children with low‐functioning ASD gestural comprehension and production using video modelling (VM) by a computer‐generated robot animation. Six to 12‐year‐old children with ASD (N = 20; IQ < 70) were taught to recognize 20 gestures produced by the robot animation (phase I), to imitate these gestures (phase II) and to produce them in appropriate social contexts (phase III). Across the three phases, significant differences were found between the results of the pretest and the immediate and follow‐up posttests; the results of both posttests were comparable, after controlling for the children's motor and visual memory skills. The children generalized their acquired gestural skills to a novel setting with a human researcher. These results suggest that VM by a robot animation is effective in teaching children with low‐functioning ASD to recognize and produce gestures.
Lay Description
What is already known about this topic:
Children with autism spectrum disorders (ASDs) have difficulties with nonverbal communication.
Children with ASD have difficulties in recognizing and producing gestures.
What this paper adds:
A multiphase therapeutic intervention program using video modelling (VM) of robot animation is effective to promoting the gestural communication skills, both recognition and production, in children with low‐functioning ASD.
Children with ASD have improved their skills to recognize the taught gestures (phase I), imitate them (phase II) and produce them in appropriate social contexts (phase III).
Children with ASD are able to generalize the acquired skills to human‐to‐human interactions after the intervention program.
Implications for practice and/or policy:
VM of a robot animation is effective in teaching children with low‐functioning ASD both gesture recognition and gesture production.
The multiphase therapeutic intervention protocol can be recommended for clinicians or teachers in special schools to teach children with low‐functioning ASD gestural communication skills.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
ABSTRACT
We report the phase-connected timing ephemeris, polarization pulse profiles, Faraday rotation measurements, and Rotating-Vector-Model (RVM) fitting results of 12 millisecond pulsars (MSPs) ...discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in the Commensal Radio Astronomy FAST survey (CRAFTS). The timing campaigns were carried out with FAST and Arecibo over 3 yr. 11 of the 12 pulsars are in neutron star–white dwarf binary systems, with orbital periods between 2.4 and 100 d. 10 of them have spin periods, companion masses, and orbital eccentricities that are consistent with the theoretical expectations for MSP–Helium white dwarf (He WD) systems. The last binary pulsar (PSR J1912−0952) has a significantly smaller spin frequency and a smaller companion mass, the latter could be caused by a low orbital inclination for the system. Its orbital period of 29 d is well within the range of orbital periods where some MSP–He WD systems have shown anomalous eccentricities, however, the eccentricity of PSR J1912−0952 is typical of what one finds for the remaining MSP–He WD systems.
Infrared photodetectors have been used extensively in biomedicine, surveillance, communication and astronomy. However, state of the art technology based on III-V and II-VI compounds still lacks ...excellent performance for high-temperature operation. Surface plasmon polaritons (SPPs) have demonstrated their capability in improving the light detection from visible to infrared wave range due to their light confinement in subwavelength scale. Advanced fabrication techniques such as electron-beam lithography (EBL) and focused ion-beam (FIB), and commercially available numerical design tool like Finite-Difference Time-Domain (FDTD) have enabled rapid development of surface plasmon (SP) enhanced photodetectors. In this review article, the basic mechanisms behind the SP-enhanced photodetection, the different type of plasmonic nanostructures utilized for enhancement, and the reported SP-enhanced infrared photodetectors will be discussed.
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FFLJ, NUK, ODKLJ, UL, UM, UPUK
We report an observation of robust suppression of edge-localized modes (ELMs) in the Experimental Advanced Superconducting Tokamak (EAST), enabled by continuous boron (B) powder injection. Edge ...harmonic oscillations appear during B powder injection, providing sufficient particle transport to maintain constant density and avoid impurity accumulation in ELM-stable plasmas. Quasi-steady ELM suppression discharges are demonstrated with modest energy confinement improvement and over a wide range of conditions: heating power and technique variation, electron density range over a factor ∼3.5, deuterium or helium ion species, and with either direction of the toroidal magnetic field. ELM suppression is observed above a threshold edge B intensity and ceases within 0.5 s of termination of the B injection. In contrast to ELM suppression accompanied by recycling reduction during Li powder injection in NSTX and EAST (Maingi et al 2018 Nucl. Fusion 58 024003), reduced recycling due to hydrogenic species retention is unnecessary for the ELM suppression with B powder injection, paving the way for its consideration as an ELM control tool for future fusion devices.
In order to determine the orbital characters on the various Fermi surface pockets of the Fe-based superconductors Ba sub(0.6)K sub(0.4)Fe sub(2)As sub(2) and FeSe sub(0.45)Te sub(0.55), we introduce ...a method to calculate photoemission matrix elements. We compare our simulations to experimental data obtained with various experimental configurations of beam orientation and light polarization. We show that the photoemission intensity patterns revealed from angle-resolved photoemission spectroscopy measurements of Fermi surface mappings and energy-momentum plots along high-symmetry lines exhibit asymmetries carrying precious information on the nature of the states probed, information that is destroyed after the data symmetrization process often performed in the analysis of angle-resolved photoemission spectroscopy data. Our simulations are consistent with Fermi surfaces originating mainly from the dxy, dxz, and dyyz orbitals in these materials.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
A model with two channels of electrical transport (TCET) for perovskite manganites is proposed, and it is described by an equivalent device with two current-carrier channels. In one channel, there is ...a spin-independent resistor (
R
3
) with an equivalent resistivity of
ρ
3
. In the other channel, there are two spin-dependent resistors in series (
R
1
and
R
2
) with an equivalent resistivity of
ρ
1
+
ρ
2
. The component
ρ
1
includes residual resistivity and the resistivity contributed by crystal-lattice scattering. The other component of the equivalent resistivity,
ρ
2
, originates from the spin orientations of the itinerant electrons and the local electrons of the outer O 2p and Mn 3d orbits that deviate from the orientation of their ground states when the test temperature is close to the Curie temperature. Using this model, we fitted the experimental curves of the resistivity
versus
test temperature for single-crystalline La
1−
x
Sr
x
MnO
3
(0.00 ≤
x
≤ 0.40) and polycrystalline La
0.6
Sr
0.4
Mn
1−
x
Fe
x
O
3
(0.00 ≤
x
≤ 0.30). In addition, we investigated the effects of the fraction of the antiferromagnetic phase, scattering at the crystallite interfaces, and the crystal-cell constants on the samples' resistivity. The physical mechanism of the TCET model was explained using an O 2p itinerant-electron model, which has been used in other studies to explain the magnetic ordering of several series of spinel ferrites and perovskite manganites.
A model with two channels of electrical transport (TCET) for perovskite manganites is proposed, and it is described by an equivalent device with two current-carrier channels.
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IJS, KILJ, NUK, UL, UM, UPUK
Abstract
PSR J2150+3427 is a 0.654 s pulsar discovered by the Commensal Radio Astronomy FAST Survey. From the follow-up observations, we find that the pulsar is in a highly eccentric orbit (
e
= ...0.601) with an orbital period of 10.592 days and a projected semimajor axis of 25.488 lt-s. Using 2.7 yr of timing data, we also measured the rate of periastron advance
ω
̇
= 0.0115(4) deg yr
−1
. An estimate for the total mass of the system using the
ω
̇
gives
M
tot
= 2.59(13)
M
⊙
, which is consistent with most of the known double neutron star (DNS) systems and one neutron star (NS)–white dwarf (WD) system named B2303+46. Combining
ω
̇
with the mass function of the system gives the masses of
M
p
< 1.67 and
M
c
> 0.98
M
⊙
for the pulsar and the companion star, respectively. This constraint, along with the spin period and orbital parameters, suggests that it is possibly a DNS system, and we cannot entirely rule out the possibility of an NS–WD system. Future timing observations will vastly improve the uncertainty in
ω
̇
, and are likely to allow the detection of additional relativistic effects, which can be used to modify the values of
M
p
and
M
c
. With a spin-down luminosity of
E
̇
= 5.07(6) × 10
29
erg s
−1
, PSR J2150+3427 is a very low-luminosity pulsar, with only the binary pulsar J2208+4610 having a smaller
E
̇
.
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