We propose a versatile framework to dynamically generate Floquet higher-order topological insulators by multistep driving of topologically trivial Hamiltonians. Two analytically solvable examples are ...used to illustrate this procedure to yield Floquet quadrupole and octupole insulators with zero- and/or π-corner modes protected by mirror symmetries. Furthermore, we introduce dynamical topological invariants from the full unitary return map and show its phase bands contain Weyl singularities whose topological charges form dynamical multipole moments in the Brillouin zone. Combining them with the topological index of a Floquet Hamiltonian gives a pair of Z_{2} invariant ν_{0} and ν_{π} which fully characterize the higher-order topology and predict the appearance of zero- and π-corner modes. Our work establishes a systematic route to construct and characterize Floquet higher-order topological phases.
Face-centered-cubic (fcc) type high entropy alloys (HEAs) exhibit outstanding ductility even at the liquid nitrogen temperature, but they are relatively weak in strength which is far from the ...requirements for practical structural applications. One of the general concepts employed previously in alloy design is the suppression of ‘brittle’ intermetallic compound formation which usually leads to a serious embrittlement. Surprisingly, we reveal in this study that the precipitation of hard σ and μ intermetallic compounds tremendously strengthened the CoCrFeNiMo0.3 HEA but without causing a serious embrittlement. It exhibits a tensile strength as high as 1.2 GPa and a good ductility of ∼19%. A careful study of the deformation behavior reveals that the fcc matrix exhibits an extremely high work hardening exponent of 0.75, which suppresses the propagation of microcracks originated at these brittle particles. Our work presents a very successful demonstration of using complex hard intermetallic particles to manipulate the properties of fcc-type HEA systems. Furthermore, lattice distortion has been carefully measured in powder-metallurgy materials by line broadening from X-ray diffraction (XRD). It is interesting to discover that lattice planes are highly distorted in HEAs and this distortion also contributes to solid solution hardening.
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Higher-order topological insulators (HOTIs) have emerged as a new class of phases, whose robust in-gap "corner" modes arise from the bulk higher-order multipoles beyond the dipoles in conventional ...topological insulators. Here, we incorporate Floquet driving into HOTIs, and report for the first time a dynamical polarization theory with anomalous nonequilibrium multipoles. Further, a proposal to detect not only corner states but also their dynamical origin in cold atoms is demonstrated, with the latter one never achieved before. Experimental determination of anomalous Floquet corner modes is also proposed.
Plasma synthesis of ammonia is a potential and sustainable way of nitrogen fixation. In this work, a series of M/Al
2
O
3
(M =Co, Ni, Co–Ni) catalysts have been investigated to enhance the synthesis ...of NH
3
from N
2
and H
2
in a dielectric barrier discharge (DBD) plasma reactor. Under the conditions of a volume ratio of N
2
:H
2
of 1:1, a total gas flow rate of 200 mL min
−1
, and a discharge temperature of 200 °C, the order of the ammonia synthesis rate filled with different catalysts was Co–Ni/Al
2
O
3
> Co/Al
2
O
3
> Ni/Al
2
O
3
> Al
2
O
3
> only plasma. And the highest ammonia synthesis rate could be obtained was 1500 μmol g
−1
h
−1
by using Co–Ni/Al
2
O
3
as the catalyst. Further research found that compared with single metal catalysis, on the one hand, the presence of Co–Ni bimetal reduced the total amount and strength of acidic sites on the catalyst surface, which is beneficial for the desorption of synthesized ammonia gas. On the other hand, the presence of Co–Ni bimetal enhanced the plasma discharge observed by the ICCD camera. At the same time, the electrical characterization was found changed with different catalysts added in the plasma synthesis process. Adding a Co–Ni bimetal loaded catalyst in the reaction system increased the average electric field (E) and improved the power efficiency.
Topological insulators are classified according to their symmetries. Discovery of them in electronic solids is thus restricted by orbital and crystalline symmetries available in nature. Synthetic ...quantum matter, such as the recent double-well optical lattices loaded with s and p orbital ultracold atoms, can exploit symmetries and interaction beyond natural conditions. Here we unveil a topological phase of interacting fermionic atoms on a two-leg ladder derived from the above experimental optical lattice by dimension reduction. The topological band structure originates from the staggered phases of sp orbital tunnelling, requiring neither spin-orbit coupling nor other known mechanisms like p-wave pairing, artificial gauge field or rotation. Upon crossing over to two-dimensional coupled ladders, the edge modes from individual ladder form a parity-protected flat band at zero energy. Experimental signatures are found in density correlations and phase transitions to trivial band and Mott insulators.
The rotation curve (RC) of the Milky Way out to ~100 kpc has been constructed using ~16,000 primary red clump giants (PRCGs) in the outer disc selected from the LAMOST Spectroscopic Survey of the ...Galactic Anti-centre (LSS-GAC) and the Sloan Digital Sky Survey (SDSS)-III/APOGEE survey, combined with ~5700 halo K giants (HKGs) selected from the SDSS/SEGUE survey. To derive the RC, the PRCG sample of the warm disc population and the HKG sample of halo stellar population are, respectively, analysed using a kinematical model allowing for the asymmetric drift corrections and re-analysed using the spherical Jeans equation along with measurements of the anisotropic parameter beta currently available. The typical uncertainties of RC derived from the PRCG and HKG samples are, respectively, 5-7 km s super( -1) and several tens km s super( -1). We determine a circular velocity at the solar position, ... and an azimuthal peculiar speed of the Sun, ..., both in good agreement with the previous determinations. The newly constructed RC has a generally flat value of 240 km s super( -1) within a Galactocentric distance rof 25 kpc and then decreases steadily to 150 km s super( -1) at r ~ 100 kpc. On top of this overall trend, the RC exhibits two prominent localized dips, one at r ~ 11 kpc and another at r ~ 19 kpc. From the newly constructed RC, combined with other constraints, we have built a parametrized mass model for the Galaxy, yielding a virial mass of the Milky Way's dark matter halo of ... and a local dark matter density, ... (ProQuest: ... denotes formulae/symbols omitted.)
Conspectus The chalcogenolato silver and copper superatoms are currently a topic of cutting edge research besides the extensively studied Au n (SR) m clusters. Crystal structure analysis is an ...indispensable tool to gain deep insights into the anatomy of these sub-nanometer clusters. The metal framework and spatial arrangement of the chalcogenolates around the metal core assist in unravelling the structure–property relationships and fundamental mechanisms involved in their fabrication. In this Account, we discuss our contribution toward the development of dichalcogenolato Ag and Cu cluster chemistry covering their fabrication and precise molecular structures. Briefly introducing the significance of the single crystal structures of the atomically precise clusters, the novel dichalcogenolated two-electron superatomic copper and its alloy systems are presented first. The Cu13{S2CNR}6{CCR′}4+ is so far the first unique copper cluster having Cu13 centered cuboctahedra, which is a miniature of bulk fcc structure. The galvanic exchange of the central Cu with Ag or Au results in a similar anatomy of formed bimetallic Au/Ag@Cu12(S2CN n Bu2)6(CCPh)4CuCl2 species. This is unique in the sense that other contemporary M13 cores in group 11 superatomic chemistry are compact icosahedra. The central doping of Ag or Au significantly affects the physiochemical properties of the bimetallic Cu-rich clusters. It is manifested in the dramatic quantum yield enhancement of the doped species Au@Cu12(S2CN n Bu2)6(CCPh)4+ with a value of 0.59 at 77 K in 2-MeTHF. In the second part, the novel eight-electron dithiophosphate- and diselenophosphate-protected silver systems are presented. A completely different type of architecture was revealed for the first time from the successful structural determination of Ag21{S2P(O i Pr)2}12+, Ag20{S2P(O i Pr)2}12 and Au@Ag19{S2P(OPr)2}12. They exhibit a nonhollow M13 (Ag or AuAg12) icosahedron, capped by 8 and 7 Ag atoms in the former and latter two species, respectively. The overall metal core units are protected by 12 dithiophosphate ligands and the metal–ligand interface structure was found to be quite different from that of Au n (SR) m . Notably, the Ag20{S2P(O i Pr)}12 cluster provides the first structural evidence of a silver superatom with a chiral metallic core. This chirality arises through the simple removal of one of capping Ag+ cations of Ag21{S2P(O i Pr)2}12+ present on its C 3 axis. Further, the effects of the ligand exchange on the structures of Ag20{Se2P(O i Pr)2}12, Ag21{Se2P(OEt)2}12+, and AuAg20{Se2P(OEt)2}12+ are studied extensively. The structure of the former species is similar to its dithiophosphate counterpart (C 3 symmetry). The latter two (T symmetry) differ in the arrangement of 8 capping Ag atoms, as they form a cube engraving the Ag13 (AuAg12) icosahedron. The blue shifts in absorption spectra and photoluminescence further indicate the strong influence of the central Au atom in the doped clusters. Finally, the first paradigm of unusual heteroatom doping induced size–structure transformations is discussed by presenting the case of formation of Au3Ag18{Se2P(O i Pr)2}12+ upon Au doping into Ag20{Se2P(O i Pr)2}120. Finally, before concluding this Account, we discuss the possibility of many unique structural isomers with different physical properties for the aforementioned Ag superatoms which need to be explored extensively in the future.
Energetic salts provide many advantages over conventional energetic molecular compounds. Their high densities, high heats of formation and low vapor pressures make them an important class of ...compounds for the development of energetic materials. More and more novel energetic ions are being obtained, but energetic cations are reported to a much lesser extent. Energetic cations develop from simple linear structures to form N-heterocyclic structures. Together with the introduction of various energetic groups, the energetic properties of energetic salts are significantly promoted. The development of energetic cations is becoming the major restriction for improving the performance of energetic salts.
Energetic cations play important roles in energetic performance, which may attribute to the diverse backbones and substituted groups of energetic cations. This review emphasizes the roles of backbones and substituted groups in the energetic performance of energetic salts.
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