Through intense research on Weyl semimetals during the past few years, we have come to appreciate that typical Weyl semimetals host many Weyl points. Nonetheless, the minimum nonzero number of Weyl ...points allowed in a time-reversal invariant Weyl semimetal is four. Realizing such a system is of fundamental interest and may simplify transport experiments. Recently, it was predicted that TaIrTe
realizes a minimal Weyl semimetal. However, the Weyl points and Fermi arcs live entirely above the Fermi level, making them inaccessible to conventional angle-resolved photoemission spectroscopy (ARPES). Here, we use pump-probe ARPES to directly access the band structure above the Fermi level in TaIrTe
. We observe signatures of Weyl points and topological Fermi arcs. Combined with ab initio calculation, our results show that TaIrTe
is a Weyl semimetal with the minimum number of four Weyl points. Our work provides a simpler platform for accessing exotic transport phenomena arising in Weyl semimetals.Weyl semimetals are interesting because they are characterized by topological invariants, but specific examples discovered to date tend to have complicated band structures with many Weyl points. Here, the authors show that TaIrTe
has only four Weyl points, the minimal number required by time-reversal symmetry.
Abstract
The recent discovery of a Weyl semimetal in TaAs offers the first Weyl fermion observed in nature and dramatically broadens the classification of topological phases. However, in TaAs it has ...proven challenging to study the rich transport phenomena arising from emergent Weyl fermions. The series Mo
x
W
1−
x
Te
2
are inversion-breaking, layered, tunable semimetals already under study as a promising platform for new electronics and recently proposed to host Type II, or strongly Lorentz-violating, Weyl fermions. Here we report the discovery of a Weyl semimetal in Mo
x
W
1−
x
Te
2
at
x
=25%. We use pump-probe angle-resolved photoemission spectroscopy (pump-probe ARPES) to directly observe a topological Fermi arc above the Fermi level, demonstrating a Weyl semimetal. The excellent agreement with calculation suggests that Mo
x
W
1−
x
Te
2
is a Type II Weyl semimetal. We also find that certain Weyl points are at the Fermi level, making Mo
x
W
1−
x
Te
2
a promising platform for transport and optics experiments on Weyl semimetals.
The near-surface part of the crust, also called the skin of the earth, is the arena of human activity of which the stiffness is of great concern to engineers in infrastructure construction. The ...stiffness reduction of near-surface geomaterials also plays a vital role in geohazards triggering. However, the physical mechanism behind the material softening is still not fully understood. Here, we report a coseismic shear-wave velocity reduction in the near surface by up to a few tens of percent during the strongest shaking from the 11 March 2011 Tohoku-Oki Earthquake and a subsequent two-stage healing process including a rapid recovery within a few minutes and a slow recovery over many years. We also present a theoretical contact model between mineral grains in geomaterials containing multiple metastable contacts at small separations due to the oscillatory hydration interaction, which can explain the emergence of different stages in the healing process.
Tin-based perovskites are the most likely alternative candidates for lead-based counterparts due to their low toxicity and excellent optoelectronic properties. However, their uncontrollable ...crystallization process limits the improvement of device performance. Here, a green anti-solvent (acetic acid, HAc) has been first applied to adjust the crystallization process of tin-based perovskites, that is, to accelerate solution nucleation by salting-out crystallization and to slow down the crystal growth rate by hydrogen bond interactions. Furthermore, the non-volatilized residual HAc reduces the loss of organic amine salts and passivates defect states in the perovskites. Consequently, a device prepared using HAc realizes the highest efficiency of 12.78% (an open circuit voltage of 0.92 V) among non-chlorobenzene-based devices. Pioneeringly, we point out a general principle that the congeners of HAc, whose ability to form a hydrogen bond is not higher than that of HAc, can act as anti-solvents to prepare tin-based perovskites.
Pioneeringly, we point out a general principle for selecting an appropriate anti-solvent. Salting-out crystallization induced by a green anti-solvent (acetic acid, HAc) has been used for the first time to fabricate Sn-based PVSCs with an efficiency of 12.78%.
Bi-atom catalysts (BACs) have attracted increasing attention in important electrocatalytic reactions such as the oxygen reduction reaction (ORR). Here, by means of density functional theory ...simulations coupled with machine-learning technology, we explored the structure-property correlation and catalytic activity origin of BACs, where metal dimers are coordinated by N-doped graphene (NC). We first sampled 26 homonuclear (M
2
/NC) BACs and constructed the activity volcano curve. Disappointingly, only one BAC, namely Co
2
/NC, exhibits promising ORR activity, leaving considerable room for enhancement in ORR performance. Then, we extended our study to 55 heteronuclear BACs (M
1
M
2
/NC) and found that 8 BACs possess competitive or superior ORR activity compared with the Pt(111) benchmark catalyst. Specifically, CoNi/NC shows the most optimal activity with a very high limiting potential of 0.88 V. The linear scaling relationships among the adsorption free energy of *OOH, *O and *OH species are significantly weakened on BACs as compared to a transition metal surface, indicating that it is difficult to precisely describe the catalytic activity with only one descriptor. Thus, we adopted machine-learning techniques to identify the activity origin for the ORR on BACs, which is mainly governed by simple geometric parameters. Our work not only identifies promising BACs yet unexplored in the experiment, but also provides useful guidelines for the development of novel and highly efficient ORR catalysts.
Bi-atom catalysts (BACs) have been tuned from homonuclear to heteronuclear bi-atom sites, giving rise to significantly enhanced ORR activity.
Topological matter is known to exhibit unconventional surface states and anomalous transport owing to unusual bulk electronic topology. In this study, we use photoemission spectroscopy and quantum ...transport to elucidate the topology of the room temperature magnet Co
MnGa. We observe sharp bulk Weyl fermion line dispersions indicative of nontrivial topological invariants present in the magnetic phase. On the surface of the magnet, we observe electronic wave functions that take the form of drumheads, enabling us to directly visualize the crucial components of the bulk-boundary topological correspondence. By considering the Berry curvature field associated with the observed topological Weyl fermion lines, we quantitatively account for the giant anomalous Hall response observed in this magnet. Our experimental results suggest a rich interplay of strongly interacting electrons and topology in quantum matter.
Necklace like-CNT/CoSe2@NC was successfully prepared via the chemical method and selenization. CNT-threaded zeolitic imidazolate framework-67 (ZIF-67) polyhedra, synthesized by wet chemical methods, ...are used as the precursor. During the selenization step, ZIF-67 polyhedra transform into mesoporous CoSe2@NC nanoclusters of nanoparticles, to form CNT-CoSe2@NC composites with a necklace-like morphology. The as-obtained necklace-like CNT/CoSe2@N-doped carbon (NC) exhibited excellent sodium ion storage performance.
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•Nanocomposite of CoSe2 and N-doped carbon threaded with carbon nanotube is synthesized.•Metal-organic framework is applied to construct necklace-like carbon nanotube composite.•Necklace-like carbon nanotube composite exhibit excellent sodium-ion storage performances.
Currently, a great challenge to the design of durable sodium-ion batteries (SIBs) is the need for the architecture of nanostructured transition metal-selenide electrodes with high capacity and excellent cycling stability. In this paper, we describe a novel metal-organic framework (MOF)-induced approach to construct necklace-like carbon nanotube (CNT)– CoSe2@N-doped carbon (NC) with excellent sodium ion storage performance. In this strategy, CNT-threaded zeolitic imidazolate framework-67 (ZIF-67) polyhedra, synthesized by wet chemical methods, are used as the precursor. During the selenization step, ZIF-67 polyhedra transform into mesoporous nanoclusters consisted of CoSe2@NC nanoparticles, forming CNT-CoSe2@NC composites with a necklace-like morphology. Such structures facilitate ion and electron transport, and inhibit the aggregation and pulverization of active materials during cycling processes via the intimate contact between the CNTs and CoSe2@NC. The as-designed composites show significantly improved electrochemical properties including high discharge capacity (404 mA·h·g−1 after 120 cycles at 0.2 A·g−1), excellent rate performance (363 mA·h·g−1 at 5.0 A·g−1), and reasonable capacity retention (80% when calculated from the 2nd cycle).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Owing to the unusual geometry of kagome lattices-lattices made of corner-sharing triangles-their electrons are useful for studying the physics of frustrated, correlated and topological quantum ...electronic states
. In the presence of strong spin-orbit coupling, the magnetic and electronic structures of kagome lattices are further entangled, which can lead to hitherto unknown spin-orbit phenomena. Here we use a combination of vector-magnetic-field capability and scanning tunnelling microscopy to elucidate the spin-orbit nature of the kagome ferromagnet Fe
Sn
and explore the associated exotic correlated phenomena. We discover that a many-body electronic state from the kagome lattice couples strongly to the vector field with three-dimensional anisotropy, exhibiting a magnetization-driven giant nematic (two-fold-symmetric) energy shift. Probing the fermionic quasi-particle interference reveals consistent spontaneous nematicity-a clear indication of electron correlation-and vector magnetization is capable of altering this state, thus controlling the many-body electronic symmetry. These spin-driven giant electronic responses go well beyond Zeeman physics and point to the realization of an underlying correlated magnetic topological phase. The tunability of this kagome magnet reveals a strong interplay between an externally applied field, electronic excitations and nematicity, providing new ways of controlling spin-orbit properties and exploring emergent phenomena in topological or quantum materials
.
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KISLJ, NUK, SBMB, UL, UM, UPUK
Inorganic films possess much higher thermoelectric performance than their organic counterparts, but their poor flexibilities limit their practical applications. Here, Sb2Te3/Tex hybrid thin films ...with high thermoelectric performance and flexibility, fabricated via a novel directional thermal diffusion reaction growth method are reported. The directional thermal diffusion enables rationally tuning the Te content in Sb2Te3, which optimizes the carrier density and leads to a significantly enhanced power factor of >20 µW cm–1 K–2, confirmed by both first‐principles calculations and experiments; while dense boundaries between Te and Sb2Te3 nanophases, contribute to the low thermal conductivity of ≈0.86 W m–1 K–1, both induce a high ZT of ≈1 in (Sb2Te3)(Te)1.5 at 453 K, ranking as the top value among the reported flexible films. Besides, thin films also exhibit extraordinary flexibility. A rationally designed flexible device composed of (Sb2Te3)(Te)1.5 thin films as p‐type legs and Bi2Te3 thin films as n‐type legs shows a high power density of >280 µW cm–2 at a temperature difference of 20 K, indicating a great potential for sustainably charging low‐power electronics.
A high ZT of ≈1 at 453 K is achieved in an inorganic Sb2Te3/Te hybrid thin film via a novel directional thermal diffusion reaction growth method with extraordinary flexibility, and the rationally designed flexible device shows a high power density by a low‐temperature difference.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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