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<jats:p> <jats:italic>Spectral beam combining is an effective way to achieve high-brightness direct diode laser output. We present an experimental study on spectral beam combining with external cavity based on transmission grating. Using a series of cylindrical transform lenses with different focal lengths, spectral beaming combining efficiency is greatly improved, and the results of wavelength intervals are consistent with the theoretical calculations. With the injection current of 90 A, a 75.1 W cw 930 nm output power with wavelength span of 18.6 nm and spectral beam combining efficiency of 92.7% is achieved, the beam parameter product is 5.77 mm⋅mrad.</jats:italic> </jats:p>

<jats:p> <jats:italic>Square microdisks with round corners are fabricated using a standard GaN-based blue LED on Si substrates. Whispering gallery-like modes in the square microdisks are investigated by finite-difference time-domain simulation. The simulation results reveal that the round corners in square microdisks can substantially suppress the number of light propagation paths and further reduce the number of optical modes. A confocal micro-photoluminescence is performed to analyze the optical properties of the square microdisks at room temperature. The single-mode dominant resonant emission is obtained in the square microdisk with corner radius of 1.5 <jats:italic>μ</jats:italic>m.</jats:italic> </jats:p>

<jats:p> <jats:italic>We propose a design of tunable double-band perfect absorbers based on the resonance absorption in acoustic metasurfaces with nesting helical tracks and deep-subwavelength thicknesses (&lt;<jats:italic>λ</jats:italic>/30 with <jats:italic>λ</jats:italic> being the operation wavelength). By rotating the cover cap with an open aperture on the nesting helical tracks, we can tailor the effective lengths of resonant tubular cavities in the absorber at will, while the absorption peak frequency is flexibly shifted in spectrum and the acoustic impedance is roughly matched with air. The simulated particle velocity fields at different configurations reveal that sound absorption mainly occurs at the open aperture. Our experiment measurements agree well with the theoretical analysis and simulation, demonstrating the wide-spectrum and tunable absorption performance of the designed flat acoustic device.</jats:italic> </jats:p>

<jats:p> <jats:italic>The propagation of acoustic waves is a fundamental topic in shallow ocean acoustics. We numerically demonstrate a three-dimensional zone of silence consisting of a circular tube with gradient index metamaterials attached to its rigid wall. The cloaking effect is verified by fine agreement with analytical calculations.</jats:italic> </jats:p>

<jats:p> <jats:italic>The Rayleigh–Taylor instability at the weakly nonlinear (WN) stage in spherical geometry is studied by numerical simulation. The mode coupling processes are revealed. The results are consistent with the WN model based on parameter expansion, while higher order effects are found to be non-negligible. For Legendre mode perturbation <jats:italic>P<jats:sub>n</jats:sub> </jats:italic>(cos<jats:italic>θ</jats:italic>), the nonlinear saturation amplitude (NSA) of the fundamental mode decreases with the mode number <jats:italic>n</jats:italic>. When <jats:italic>n</jats:italic> is large, the spherical NSA is lower than the corresponding planar one. However, for large <jats:italic>n</jats:italic>, the planar NSA can be recovered by applying Fourier transformation to the bubble/spike near the equator and calculating the NSA of the converted trigonometric harmonic.</jats:italic> </jats:p>

<jats:p> <jats:italic>Apatite ceramics Ca<jats:sub>10</jats:sub>(PO<jats:sub>4</jats:sub>)<jats:sub>6</jats:sub> <jats:italic>X</jats:italic> <jats:sub>2</jats:sub> (<jats:italic>X</jats:italic> = <jats:italic>F</jats:italic>, <jats:italic>OH</jats:italic>) were prepared by the standard solid state sintering method and irradiated with He ions under a fluence of 5 × 10<jats:sup>16</jats:sup> ions/cm<jats:sup>2</jats:sup> at 450 °C. Irradiation induced formation and growth of the He bubbles were observed by a transmission electron microscope. Hydroxyapatite Ca<jats:sub>10</jats:sub>(PO<jats:sub>4</jats:sub>)<jats:sub>6</jats:sub>(OH)<jats:sub>2</jats:sub> and fluoroapatite Ca<jats:sub>10</jats:sub>(PO<jats:sub>4</jats:sub>)<jats:sub>6</jats:sub>F<jats:sub>2</jats:sub> with different He bubble morphologies indicate the influence of <jats:italic>OH</jats:italic> <jats:sup>–</jats:sup>/<jats:italic>F</jats:italic> <jats:sup>–</jats:sup> substitution on the He-ion annealing efficiency, as well as the structure itself, which affects the process of He bubble evolution and formation. The grain boundaries also act as sinks to accumulate He bubbles. No obvious irradiation damage but slight intensity reduction and left shift of diffraction peaks were observed according to the grazing incidence x-ray diffraction and Raman spectra characterizations, indicating that defects of interstitials and vacancies were generated.</jats:italic> </jats:p>

<jats:p> <jats:italic>Employing Monte Carlo simulations based on the cluster expansion, the special quasi-random structures and first-principles calculations, we systematically investigate the structure transition of BeZnO<jats:sub>2</jats:sub> alloys from the ordered to the disordered phase driven by the increased synthesis temperature, together with the solid-state phase diagram. It is found that by controlling the ordering parameter at the mixed sublattice, the band structure can vary continuously from a wide direct band gap of 4.61 eV for the fully ordered structure to a relatively narrow direct band gap of 3.60 eV for the fully disordered structure. Therefore, a better optical performance could be achieved simply by controlling the synthesis temperature, which determines the ordering parameters and thus the band gaps.</jats:italic> </jats:p>

<jats:p> <jats:italic>Three-dimensional (3D) topological insulators (TIs) are candidate materials for various electronic and spintronic devices due to their strong spin-orbit coupling and unique surface electronic structure. Rapid, low-cost preparation of large-area TI thin films compatible with conventional semiconductor technology is the key to the practical applications of TIs. Here we show that wafer-sized Bi</jats:italic> <jats:sub>2</jats:sub> <jats:italic>Te</jats:italic> <jats:sub>3</jats:sub> <jats:italic>family TI and magnetic TI films with decent quality and well-controlled composition and properties can be prepared on amorphous SiO</jats:italic> <jats:sub>2</jats:sub> <jats:italic>/Si substrates by magnetron cosputtering. The SiO</jats:italic> <jats:sub>2</jats:sub> <jats:italic>/Si substrates enable us to electrically tune</jats:italic> (<jats:italic>Bi</jats:italic> <jats:sub>1–<jats:italic>x</jats:italic> </jats:sub> <jats:italic>Sb<jats:sub>x</jats:sub> </jats:italic>)<jats:sub>2</jats:sub> <jats:italic>Te</jats:italic> <jats:sub>3</jats:sub> <jats:italic>and Cr-doped</jats:italic> (<jats:italic>Bi</jats:italic> <jats:sub>1–x</jats:sub> <jats:italic>Sb<jats:sub>x</jats:sub> </jats:italic>)<jats:sub>2</jats:sub> <jats:italic>Te</jats:italic> <jats:sub>3</jats:sub> <jats:italic>TI films between p-type and n-type behavior and thus study the phenomena associated with topological surface states, such as the quantum anomalous Hall effect (QAHE). This work significantly facilitates the fabrication of TI-based devices for electronic and spintronic applications.</jats:italic> </jats:p>

<jats:p>Single crystal rare-earth magnets, such as hexagonal-close-packed gadolinium, usually have a large second order anisotropy <jats:italic>K</jats:italic> <jats:sub>2</jats:sub> and a negative first order anisotropy <jats:italic>K</jats:italic> <jats:sub>1</jats:sub> at low temperatures, which are difficult to explain using microscopic theories. An atomic scale effective spin Hamiltonian <jats:italic>ℱ</jats:italic>[{<jats:italic> <jats:bold>S</jats:bold> <jats:sub>i</jats:sub> </jats:italic>}] is proposed, which, apart from the usual isotropic nearest neighbor coupling <jats:italic>J</jats:italic>, consists of two new terms that are different for in-plane and out-of-plane neighbors and which are characterized by two new couplings <jats:italic>C</jats:italic> <jats:sub>1</jats:sub> and <jats:italic>C</jats:italic> <jats:sub>2</jats:sub>, respectively. The hybrid Monte–Carlo method is utilized to sample this system to the desired Boltzmann-like distribution exp(−<jats:italic>ℱ</jats:italic>/<jats:italic>k</jats:italic> <jats:sub>B</jats:sub> <jats:italic>T</jats:italic>). It is found that <jats:italic>K</jats:italic> <jats:sub>2</jats:sub> and <jats:italic>K</jats:italic> <jats:sub>1</jats:sub> are compatible with the experimental values and arise naturally from the exchange anisotropy <jats:italic>C</jats:italic> <jats:sub>1</jats:sub> and <jats:italic>C</jats:italic> <jats:sub>2</jats:sub>, which are less than 0.01 in magnitude of the isotropic exchange energy <jats:italic>J</jats:italic>. This new model spin Hamiltonian can also be applied to study other magnetic properties.</jats:p>

<jats:p> <jats:italic>We report a quantum Monte Carlo study of the phase transition between antiferromagnetic and valence-bond solid ground states in the square-lattice <jats:italic>S</jats:italic> = 1/2 <jats:italic>J</jats:italic>–<jats:italic>Q</jats:italic> model. The critical correlation function of the <jats:italic>Q</jats:italic> terms gives a scaling dimension corresponding to the value <jats:italic>ν</jats:italic> = 0.455 ± 0.002 of the correlation-length exponent. This value agrees with previous (less precise) results from conventional methods, e.g., finite-size scaling of the near-critical order parameters. We also study the <jats:italic>Q</jats:italic>-derivatives of the Binder cumulants of the order parameters for <jats:italic>L</jats:italic> <jats:sup>2</jats:sup> lattices with <jats:italic>L</jats:italic> up to 448. The slope grows as <jats:italic>L</jats:italic> <jats:sup>1/<jats:italic>ν</jats:italic> </jats:sup> with a value of <jats:italic>ν</jats:italic> consistent with the scaling dimension of the <jats:italic>Q</jats:italic> term. There are no indications of runaway flow to a first-order phase transition. The mutually consistent estimates of <jats:italic>ν</jats:italic> provide compelling support for a continuous deconfined quantum-critical point.</jats:italic> </jats:p>