173 research outputs found
Local breaking of four-fold rotational symmetry by short-range magnetic order in heavily overdoped Ba(FeCu)As
We investigate Cu-doped Ba(FeCu)As with transport,
magnetic susceptibility, and elastic neutron scattering measurements. In the
heavily Cu-doped regime where long-range stripe-type antiferromagnetic order in
BaFeAs is suppressed, Ba(FeCu)As (0.145 0.553) samples exhibit spin-glass-like behavior in magnetic
susceptibility and insulating-like temperature dependence in electrical
transport. Using elastic neutron scattering, we find stripe-type short-range
magnetic order in the spin-glass region identified by susceptibility
measurements. The persistence of short-range magnetic order over a large doping
range in Ba(FeCu)As likely arises from local arrangements
of Fe and Cu that favor magnetic order, with Cu acting as vacancies relieving
magnetic frustration and degeneracy. These results indicate locally broken
four-fold rotational symmetry, suggesting that stripe-type magnetism is
ubiquitous in iron pnictides.Comment: accepted by Physical Review B Rapid Communication
Enhanced mechanical, thermal and flame retardant properties by combining graphene nanosheets and metal hydroxide nanorods for Acrylonitrile–Butadiene–Styrene copolymer composite
Three metal hydroxide nanorods (MHR) with uniform diameters were synthesized, and then combined with graphene nanosheets (GNS) to prepare acrylonitrile–butadiene–styrene (ABS) copolymer composites. An excellent dispersion of exfoliated two-dimensional (2-D) GNS and 1-D MHR in the ABS matrix was achieved. The effects of combined GNS and MHR on the mechanical, thermal and flame retardant properties of the ABS composites were investigated. With the addition of 2 wt% GNS and 4 wt% Co(OH)2, the tensile strength, bending strength and storage modulus of the ABS composites were increased by 45.1%, 40.5% and 42.3% respectively. The ABS/GNS/Co(OH)2 ternary composite shows the lowest maximum weight loss rate and highest residue yield. Noticeable reduction in the flammability was achieved with the addition of GNS and Co(OH)2, due to the formation of more continuous and compact charred layers that retarded the mass and heat transfer between the flame and the polymer matrix
Nature of the spin resonance mode in CeCoIn
Spin-fluctuation-mediated unconventional superconductivity can emerge at the
border of magnetism, featuring a superconducting order parameter that changes
sign in momentum space. Detection of such a sign-change is experimentally
challenging, since most probes are not phase-sensitive. The observation of a
spin resonance mode (SRM) from inelastic neutron scattering is often seen as
strong phase-sensitive evidence for a sign-changing superconducting order
parameter, by assuming the SRM is a spin-excitonic bound state. Here, we show
that for the heavy fermion superconductor CeCoIn, its SRM defies
expectations for a spin-excitonic bound state, and is not a manifestation of
sign-changing superconductivity. Instead, the SRM in CeCoIn likely arises
from a reduction of damping to a magnon-like mode in the superconducting state,
due to its proximity to magnetic quantum criticality. Our findings emphasize
the need for more stringent tests of whether SRMs are spin-excitonic, when
using their presence to evidence sign-changing superconductivity.Comment: accepted for publication in Communications Physic
Effects of Using Aluminum Sulfate as an Accelerator and Acrylic Acid, Aluminum Fluoride, or Alkanolamine as a Regulator in Early Cement Setting
Aluminum sulfate was employed as the main accelerator in order to explore new non-chloride and alkali-free cement accelerators. Acrylic acid, aluminum fluoride, or alkanolamine were used as regulators to further accelerate cement setting. The setting time, compressive, and flexural strengths in cement early strength progress were detected, and both the cement (raw material) and hydrated mortar were fully characterized. The cement setting experiments revealed that only loading acrylic acid as the regulator would decrease the setting time of cement and increase the compressive and flexural strengths of mortar, but further introduction of aluminum fluoride or alkanolamine improved this process drastically. In the meantime, structural characterizations indicated that the raw material (cement) used in this work was composed of C3S (alite), while hydrated mortar consisted of quartz and C3A (tricalcium aluminate). During this transformation, the coordination polyhedron of Al3+ was changed from a tetrahedron to octahedron. This work puts forward a significant strategy for promoting the activity of aluminum sulfate in cement setting and would contribute to the future design of new non-chloride and alkali-free cement accelerators
Using Verb Extension to Gauge Children’s Verb Meaning Construals: The Case of Chinese
Verb extension is a crucial gauge of the acquisition of verb meaning. In English, studies suggest that young children show conservative extension. An important test of whether an early conservative extension is a general phenomenon or a function of the input language is made possible by Chinese, a language in which verbs are more frequent and acquired earlier. This study tested whether 3-year-old Chinese children extended a group of familiar verbs that specify various ways to carry objects. Shown videos that portrayed typical, mid-typical, or atypical carrying actions (as verified by Chinese adults), children were asked to judge whether they were examples of specific Chinese carry verbs. Children’s verb extensions were mostly limited to typical exemplars, suggesting that an early conservative extension may be universal. Furthermore, extension breadth was related to the onset of verb production: verbs acquired earlier elicited more extension judgments than those acquired later
Dynamic spin-lattice coupling and nematic fluctuations in NaFeAs
We use inelastic neutron scattering to study acoustic phonons and spin
excitations in single crystals of NaFeAs, a parent compound of iron pnictide
superconductors. NaFeAs exhibits a tetragonal-to-orthorhombic structural
transition at K and a collinear antiferromagnetic (AF) order at
K. While longitudinal and out-of-plane transverse acoustic
phonons behave as expected, the in-plane transverse acoustic phonons reveal
considerable softening on cooling to , and then harden on approaching
before saturating below . In addition, we find that spin-spin
correlation lengths of low-energy magnetic excitations within the FeAs layer
and along the -axis increase dramatically below , and show weak anomaly
across . These results suggest that the electronic nematic phase present
in the paramagnetic tetragonal phase is closely associated with dynamic
spin-lattice coupling, possibly arising from the one-phonon-two-magnon
mechanism
Spin excitations and the Fermi surface of superconducting FeS
High-temperature superconductivity occurs near antiferromagnetic
instabilities and nematic state. Debate remains on the origin of nematic order
in FeSe and its relation with superconductivity. Here, we use transport,
neutron scatter- ing and Fermi surface measurements to demonstrate that
hydro-thermo grown superconducting FeS, an isostructure of FeSe, is a
tetragonal paramagnet without nematic order and with a quasiparticle mass
significantly reduced from that of FeSe. Only stripe-type spin excitation is
observed up to 100 meV. No direct coupling between spin excitation and
superconductivity in FeS is found, suggesting that FeS is less correlated and
the nematic order in FeSe is due to competing checkerboard and stripe spin
fluctuations.Comment: 11 pages, 4 page
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