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<jats:p>We investigate the properties of Bose–Einstein condensates (BECs) in a two-dimensional quasi-periodic optical lattice (OL) with eightfold rotational symmetry by numerically solving the Gross–Pitaevskii equation. In a stationary external harmonic trapping potential, we first analyze the evolution of matter-wave interference pattern from periodic to quasi-periodic as the OL is changed continuously from four-fold periodic to eight-fold quasi-periodic. We also investigate the transport properties during this evolution for different interatomic interaction and lattice depth, and find that the BEC crosses over from ballistic diffusion to localization. Finally, we focus on the case of eightfold symmetric lattice and consider a global rotation imposed by the external trapping potential. The BEC shows vortex pattern with eightfold symmetry for slow rotation, becomes unstable for intermediate rotation, and exhibits annular solitons with approximate axial symmetry for fast rotation. These results can be readily demonstrated in experiments using the same configuration as in <jats:italic>Phys. Rev. Lett.</jats:italic> <jats:bold>122</jats:bold> 110404 (2019).</jats:p>

<jats:p>Based on first-principles simulations, we revisit the crystal structures, electronic structures, and structural stability of the layered transition metal dichalcogenides (TMDCs) NbS<jats:sub>2</jats:sub>, and shed more light on the crucial roles of the van der Waals (vdW) interactions. Theoretically calculated results imply that the vdW corrections are important to reproduce the layered crystal structure, which is significant to correctly describe the electronic structure of NbS<jats:sub>2</jats:sub>. More interestingly, under hydrostatic pressure or tensile strain in <jats:italic>ab</jats:italic> plane, an isostructural phase transition from two-dimensional layered structure to three-dimensional bulk in the <jats:italic>I</jats:italic>4/<jats:italic>mmm</jats:italic> phase has been uncovered. The abnormal structural transition is closely related to the electronic structure instability and interlayer bonding effects. The interlayer Nb–S distances collapse and the interlayer vdW interactions disappear, concomitant with new covalent bond emerging and increasing coordination number. Present work highlights the significance of the vdW interactions, and provides new insights on the unconventional structural transitions in NbS<jats:sub>2</jats:sub>, which will attract wide audience working in the hectic field of TMDCs.</jats:p>

<jats:p>Ni<jats:sub>50</jats:sub>Mn<jats:sub>25</jats:sub>Ga<jats:sub>20</jats:sub>Fe<jats:sub>5</jats:sub> ferromagnetic shape memory alloy microwires with diameters of ∼ 30–50 μm and grain sizes of ∼ 2–5 μm were prepared by melt-extraction technique. A step-wise chemical ordering annealing was carried out to improve the superelasticity strain and recovery ratio which were hampered by the internal stress, compositional inhomogeneity, and high-density defects in the as-extracted Ni<jats:sub>50</jats:sub>Mn<jats:sub>25</jats:sub>Ga<jats:sub>20</jats:sub>Fe<jats:sub>5</jats:sub> microwires. The annealed microwires exhibited enhanced atomic ordering degree, narrow thermal hysteresis, and high saturation magnetization under a low magnetic field. As a result, the annealed microwire showed decreased superelastic critical stress, improved reversibility, and a high superelastic strain (1.9%) with a large recovery ratio (&gt; 96%). This kind of filamentous material with superior superelastic effects may be promising materials for minor-devices.</jats:p>

<jats:p>The layered magnetic van der Waals materials have generated tremendous interest due to their potential applications and importance in fundamental research. Previous x-ray diffraction (XRD) studies on the magnetic van der Waals compound VI<jats:sub>3</jats:sub>, revealed a structural transition above the magnetic transition but output controversial analysis on symmetry. In this paper we carried out polarized Raman scattering measurements on VI<jats:sub>3</jats:sub> from 10 K to 300 K, with focus on the two <jats:italic>A</jats:italic> <jats:sub>g</jats:sub> phonon modes at ∼ 71.1 cm<jats:sup>−1</jats:sup> and 128.4 cm<jats:sup>−1</jats:sup>. Our careful symmetry analysis based on the angle-dependent spectra demonstrates that the crystal symmetry can be well described by <jats:italic>C</jats:italic> <jats:sub>2<jats:italic>h</jats:italic> </jats:sub> rather than <jats:italic>D</jats:italic> <jats:sub>3<jats:italic>d</jats:italic> </jats:sub> both above and below structural phase transition. We further performed temperature-dependent Raman experiments to study the magnetism in VI<jats:sub>3</jats:sub>. Fano asymmetry and anomalous linewidth drop of two <jats:italic>A</jats:italic> <jats:sub>g</jats:sub> phonon modes at low temperatures, point to a significant spin–phonon coupling. This is also supported by the softening of 71.1-cm<jats:sup>−1</jats:sup> mode above the magnetic transition. The study provides the fundamental information on lattice dynamics and clarifies the symmetry in VI<jats:sub>3</jats:sub>. And spin–phonon coupling existing in a wide temperature range revealed here may be meaningful in applications.</jats:p>

<jats:p>A small amount of Ni was added into the binary Gd<jats:sub>50</jats:sub>Co<jats:sub>50</jats:sub> amorphous alloy to replace Gd in order to obtain ternary Co<jats:sub>50</jats:sub>Gd<jats:sub>50 − <jats:italic>x</jats:italic> </jats:sub>Ni<jats:sub> <jats:italic>x</jats:italic> </jats:sub> (<jats:italic>x</jats:italic> = 1, 2, and 3) amorphous alloys. Compared to the binary Gd<jats:sub>50</jats:sub>Co<jats:sub>50</jats:sub> amorphous alloy, the Co<jats:sub>50</jats:sub>Gd<jats:sub>50 − <jats:italic>x</jats:italic> </jats:sub>Ni<jats:sub> <jats:italic>x</jats:italic> </jats:sub> amorphous alloys show an enhanced Curie temperature (<jats:italic>T</jats:italic> <jats:sub>C</jats:sub>) with a weakened formability. The maximum magnetic entropy change (<jats:inline-formula> <jats:tex-math><?CDATA $-\Delta {S}_{{\rm{m}}}^{{\rm{peak}}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>−</mml:mo> <mml:mo>Δ</mml:mo> <mml:msubsup> <mml:mi>S</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">peak</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_5_056401_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) of the Co<jats:sub>50</jats:sub>Gd<jats:sub>50−<jats:italic>x</jats:italic> </jats:sub>Ni<jats:sub> <jats:italic>x</jats:italic> </jats:sub> amorphous alloys is found to decrease with the increasing <jats:italic>T</jats:italic> <jats:sub>C</jats:sub>. The adiabatic temperature rise (Δ<jats:italic>T</jats:italic> <jats:sub>ad</jats:sub>) of the Co<jats:sub>50</jats:sub>Gd<jats:sub>47</jats:sub>Ni<jats:sub>3</jats:sub> amorphous alloy is superior to that of the Fe-based metallic glasses at room temperature. The variation of the <jats:italic>T</jats:italic> <jats:sub>C</jats:sub> and <jats:inline-formula> <jats:tex-math><?CDATA $-\Delta {S}_{{\rm{m}}}^{{\rm{peak}}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>−</mml:mo> <mml:mo>Δ</mml:mo> <mml:msubsup> <mml:mi>S</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">peak</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_5_056401_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> of the Gd<jats:sub>50</jats:sub>Co<jats:sub>50</jats:sub> amorphous alloy with Ni addition, and the mechanism involved, were discussed.</jats:p>

<jats:p>Epitaxial growth and structural characteristics of metastable <jats:italic>β</jats:italic>-In<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> thin films on H-terminated Si(111) substrates are studied. The In<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> thin films grown below the <jats:italic>β</jats:italic>-to-<jats:italic>α</jats:italic> phase transition temperature (453 K) are characterized to be strained <jats:italic>β</jats:italic>-In<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> mixed with significant <jats:italic>γ</jats:italic>-In<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> phases. The pure-phased single-crystalline <jats:italic>β</jats:italic>-In<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> can be reproducibly achieved by <jats:italic>in situ</jats:italic> annealing the as-deposited poly-crystalline In<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> within the phase equilibrium temperature window of <jats:italic>β</jats:italic>-In<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub>. It is suggeted that the observed <jats:italic>γ</jats:italic>-to-<jats:italic>β</jats:italic> phase transition triggered by quite a low annealing temperature should be a rather lowered phase transition barrier of the epitaxy-stabilized In<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> thin-film system at a state far from thermodynamic equilibrium.</jats:p>

<jats:p>Adsorption of chalcogen atoms on metal surfaces has attracted increasing interest for both the fundamental research and industrial applications. Here, we report a systematic study of selenium (Se) adsorption on Au(111) at varies substrate temperatures by scanning tunneling microscopy. At room temperature, small Se clusters are randomly dispersed on the surface. Increasing the temperature up to 200 °C, a well-ordered lattice of Se molecules consisting of 8 Se atoms in ring-like structure is formed. Further increasing the temperature to 250 °C gives rise to the formation of Se monolayer with Au(111)-<jats:inline-formula> <jats:tex-math> <?CDATA $\sqrt{3}\times \sqrt{3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msqrt> <mml:mn>3</mml:mn> </mml:msqrt> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mn>3</mml:mn> </mml:msqrt> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_5_056801_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> lattices superimposed with a quasi-hexagonal lattice. Desorption of Se atoms rather than the reaction between the Se atoms and the Au substrate occurs if further increasing the temperature. The ordered structures of selenium monolayers could serve as templates for self-assemblies and our findings in this work might provide insightful guild for the epitaxial growth of the two-dimensional transition metal dichalcogenides.</jats:p>

<jats:p>Localized surface plasmonic resonance has attracted extensive attention since it allows for great enhancement of local field intensity on the nanoparticle surface. In this paper, we make a systematic study on the excitation of localized surface plasmons of a graphene coated dielectric particle. Theoretical results show that both the intensity and frequency of the plasmonic resonant peak can be tuned effectively through modifying the graphene layer. Furthermore, high order localized surface plasmons could be excited and tuned selectively by the Laguerre Gaussian beam, which is induced by the optical angular orbital momentum transfer through the mutual interaction between the particle and the helical wavefront. Moreover, the profiles of the multipolar localized surface plasmons are illustrated in detail. The study provides rich potential applications in the plasmonic devices and the wavefront engineering nano-optics.</jats:p>

<jats:p>Most three-dimensional (3D) and two-dimensional (2D) boron nitride (BN) structures are wide-band-gap insulators. Here, we propose two BN monolayers having Dirac points and flat bands, respectively. One monolayer is named as 5–7 BN that consists of five- and seven-membered rings. The other is a Kagome BN made of triangular boron rings and nitrogen dimers. The two structures show not only good dynamic and thermodynamic stabilities but also novel electronic properties. The 5–7 BN has Dirac points on the Fermi level, indicating that the structure is a typical Dirac material. The Kagome BN has double flat bands just below the Fermi level, and thus there are heavy fermions in the structure. The flat-band-induced ferromagnetism is also revealed. We analyze the origination of the band structures by partial density of states and projection of orbitals. In addition, a possible route to experimentally grow the two structures on some suitable substrates such as the PbO<jats:sub>2</jats:sub> (111) surface and the CdO (111) surface is also discussed, respectively. Our research not only extends understanding on the electronic properties of BN structures, but also may expand the applications of BN materials in 2D electronic devices.</jats:p>