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<jats:p>We use quantum Monte Carlo simulations to study an <jats:italic>S</jats:italic> = 1/2 spin model with competing multi-spin interactions. We find a quantum phase transition between a columnar valence-bond solid (cVBS) and a Néel antiferromagnet (AFM), as in the scenario of deconfined quantum-critical points, as well as a transition between the AFM and a staggered valence-bond solid (sVBS). By continuously varying a parameter, the sVBS–AFM and AFM–cVBS boundaries merge into a direct sVBS–cVBS transition. Unlike previous models with putative deconfined AFM–cVBS transitions, e.g., the standard <jats:italic>J</jats:italic>–<jats:italic>Q</jats:italic> model, in our extended <jats:italic>J</jats:italic>–<jats:italic>Q</jats:italic> model with competing cVBS and sVBS inducing terms the transition can be tuned from continuous to first-order. We find the expected emergent U(1) symmetry of the microscopically <jats:italic>Z</jats:italic> <jats:sub>4</jats:sub> symmetric cVBS order parameter when the transition is continuous. In contrast, when the transition changes to first-order, the clock-like <jats:italic>Z</jats:italic> <jats:sub>4</jats:sub> fluctuations are absent and there is no emergent higher symmetry. We argue that the confined spinons in the sVBS phase are fracton-like. We also present results for an SU(3) symmetric model with a similar phase diagram. The new family of models can serve as a useful tool for further investigating open questions related to deconfined quantum criticality and its associated emergent symmetries.</jats:p>

<jats:p>We report the successful synthesis of a new diluted magnetic semiconductor (Ca,Na)(Zn,Mn)<jats:sub>2</jats:sub>Sb<jats:sub>2</jats:sub>. Na and Mn are doped into the parent compound CaZn<jats:sub>2</jats:sub>Sb<jats:sub>2</jats:sub>, which has the same crystal structure as that of “122” type iron-based superconductor CaFe<jats:sub>2</jats:sub>As<jats:sub>2</jats:sub>. Na substitution for Ca and Mn substitution for Zn introduce carriers and spins, respectively. Doping Mn atoms alone up to 5% does not induce any type of magnetic ordering. When both Na and Mn are co-doped, a ferromagnetic ordering with maximum <jats:italic>T</jats:italic> <jats:sub>C</jats:sub> ∼ 10 K has been observed. Iso-thermal magnetization shows that the coercive field is up to ∼ 245 Oe at 2 K. Below <jats:italic>T</jats:italic> <jats:sub>C</jats:sub>, a negative magneto-resistance with MR ∼ 12% has also been achieved.</jats:p>

<jats:p>A variable-<jats:italic>K</jats:italic> trenches silicon-on-insulator (SOI) lateral diffused metal–oxide–semiconductor field-effect transistor (MOSFET) with a double conductive channel is proposed based on the enhancement of low dielectric constant media to electric fields. The device features variable-<jats:italic>K</jats:italic> dielectric double trenches and a P-pillar between the trenches (VK DT-P LDMOS). The low-<jats:italic>K</jats:italic> dielectric layer on the surface increases electric field of it. Adding a variable-<jats:italic>K</jats:italic> material introduces a new electric field peak to the drift region, so as to optimize electric field inside the device. Introduction of the high-concentration vertical P-pillar between the two trenches effectively increases doping concentration of the drift region and maintains charge balance inside it. Thereby, breakdown voltage (<jats:italic>BV</jats:italic>) of the device is increased. The double conductive channels provide two current paths that significantly reduce specific on-resistance (<jats:italic>R</jats:italic> <jats:sub>on,sp</jats:sub>). Simulation results demonstrate that a 17-μm-length device can achieve a <jats:italic>BV</jats:italic> of 554 V and a low on-resistance of 13.12 mΩ⋅cm<jats:sup>2</jats:sup>. The <jats:italic>R</jats:italic> <jats:sub>on,sp</jats:sub> of VK DT-P LDMOS is reduced by 78.9% compared with the conventional structure.</jats:p>

<jats:p>Effect of heating time on the structural, morphology, optical, and photocatalytic properties of graphitic carbon nitride (g-C<jats:sub>3</jats:sub>N<jats:sub>4</jats:sub>) nanosheets prepared at 550 °C in Ar atmosphere is studied. The investigations are carried out by using x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), UV–vis absorption, and photoluminescence (PL). At a heating temperature of 550 °C, g-C<jats:sub>3</jats:sub>N<jats:sub>4</jats:sub> nanocrystals are formed after 0.5 h and become more orderly as the heating time increases. The surface area of the g-C<jats:sub>3</jats:sub>N<jats:sub>4</jats:sub> nanosheets significantly increases as the preparation time increases. The g-C<jats:sub>3</jats:sub>N<jats:sub>4</jats:sub> prepared in 2.5 h shows the highest photocatalytic performance, decomposing completely 10 ppm RhB solution under xenon lamp irradiation for 2.0 h.</jats:p>

<jats:p>We applied the finite element method to calculate the extinction spectrum of single hyperbolic hexagonal boron nitride (h-BN) nanodisk. We show that the hyperbolic h-BN nanodisk exhibits two extinction mechanisms in the mid-infrared region. The volume confined phonon polaritons resonances of the nanodisk give rise to a series of weak extinction peaks. The localized surface phonon polaritons lead to a robust dipolar extinction, and the extinction peak position is tunable by varying the size of the h-BN nanodisk. These findings reveal the mechanisms of the interaction between light and resonant h-BN nanodisk, which are essential for h-BN related opto-electromagnetic applications.</jats:p>

<jats:p>Terahertz (THz) waves have shown a broad prospect in the analysis of some dielectric materials because of their special properties. For the ultrafast irreversible processes, the THz single-shot measurement is a good choice. In this paper, a single-shot system is investigated, where a pump beam is used to generate THz pulses with high electrical field by optical rectification in LiNbO<jats:sub>3</jats:sub>, the probe beam with wavefront tilted by a blazed grating is used for single-shot measurement. The time window is up to 90 ps, the signal to noise ratio is 2000 : 1, the spectrum covers from 0.1 THz to about 2.0 THz, and the spectral resolution is 0.011 THz. The single-shot measurement result agrees well with that of a traditional electrical-optic sampling method.</jats:p>

<jats:p>According to time-dependent density functional theory (TDDFT), we study the interactions between ultra-fast laser pulses and two kinds of calcium titanate quantum dots (PCTO-QDs and MCTO-QDs). Under the action of localized field effect, ultrafast laser can induce quantum dots to make the transition from insulator to metal. The PCTO-QDs are ultimately metallic, while the MCTO-QDs are still insulator after experiencing metal state. This is bacause the stability of the unsaturated atoms in the outermost layer of PCTO-QDs is weak and the geometric configuration of MCTO-QDs as a potential well will also reduce the damage of laser. Moreover, laser waveforms approaching to the intrinsic frequency of quantum dots tend to cause the highest electron levels to cross the Fermi surface. In this paper, it is reported that the insulating quantum dots can be transformed into metal by adjusting the intensity and frequency of laser. The importance of local morphology is emphasized by comparing two kinds of CTO-QDs. More importantly, it is an important step to identify the potential properties of perovskite materials.</jats:p>

<jats:p>The Mg acceptor activation mechanism and hole transport characteristics in AlGaN alloy with Mg doping concentration (∼ 10<jats:sup>20</jats:sup> cm<jats:sup>−3</jats:sup>) grown by metal–organic chemical vapor deposition (MOCVD) are systematically studied through optical and electrical properties. Emission lines of shallow oxygen donors and (V<jats:sub>III</jats:sub> complex)<jats:sup>1−</jats:sup> as well as <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{V}}}_{{\rm{N}}}^{3+}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi mathvariant="normal">V</mml:mi> <mml:mi mathvariant="normal">N</mml:mi> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_5_058103_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and neutral Mg acceptors are observed, which indicate that self-compensation is occurred in Mg-doped AlGaN at highly doping levels. The fitting of the temperature-dependent Hall effect data shows that the acceptor activation energy values in Mg-doped Al<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Ga<jats:sub>1 − <jats:italic>x</jats:italic> </jats:sub>N (<jats:italic>x</jats:italic> = 0.23, 0.35) are 172 meV and 242 meV, and the hole concentrations at room temperature are 1.2 × 10<jats:sup>18</jats:sup> cm<jats:sup>−3</jats:sup> and 3.3 × 10<jats:sup>17</jats:sup> cm<jats:sup>−3</jats:sup>, respectively. Therefore, it is believed that there exists the combined effect of the Coulomb potentials of the dopants and screening of the Coulomb potentials by a high hole concentration. Moreover, due to the high ionized acceptors’ concentration and compensation ratio, the impurity conduction becomes more prominent and the valence band mobility drops sharply at low temperature.</jats:p>

<jats:p>Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention because of their unique properties and great potential in nano-technology applications. Great efforts have been devoted to fabrication of novel structured TMD monolayers by modifying their pristine structures at the atomic level. Here we propose an intriguing structured 1T-PtTe<jats:sub>2</jats:sub> monolayer as hydrogen evolution reaction (HER) catalyst, namely, Pt<jats:sub>4</jats:sub>Te<jats:sub>7</jats:sub>, using first-principles calculations. It is found that Pt<jats:sub>4</jats:sub>Te<jats:sub>7</jats:sub> is a stable monolayer material verified by the calculation of formation energy, phonon dispersion, and <jats:italic>ab initio</jats:italic> molecular dynamics simulations. Remarkably, the novel structured void-containing monolayer exhibits superior catalytic activity toward HER compared with the pristine one, with a Gibbs free energy very close to zero (less than 0.07 eV). These features indicate that Pt<jats:sub>4</jats:sub>Te<jats:sub>7</jats:sub> monolayer is a high-performance HER catalyst with a high platinum utilization. These findings open new perspectives for the functionalization of 2D TMD materials at an atomic level and its application in HER catalysis.</jats:p>