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<jats:p>Two-dimensional (2D) blue phosphorene with a honeycomb structure is the phosphorus analog of graphene, and is regarded as a promising 2D material with a large tunable band gap and high charge-carrier mobility. Here, using the molecular beam epitaxy method, we synthesize monolayer blue phosphorene on the Ag(111) surface. Combined with first-principles calculations, scanning tunneling microscopy measurements reveal that the blue phosphorene on the Ag(111) surface consists of 2D clusters with a buckling 1 × 1 lattice, arranged regularly on the Ag(111). The formation of these phosphorus clusters stems from the strain modulation induced by the lattice mismatch between blue phosphorene and the Ag(111) substrate. Moreover, x-ray photoelectron spectroscopy measurements are performed to study the instability of the blue phosphorene clusters in air. The realization of regular nanoclusters of blue phosphorene with unique sizes and morphology provides an ideal platform for the exploration of the quantum physical properties and applications of blue phosphorene.</jats:p>

<jats:p>This paper proposes a method of repairing interface defects by supercritical nitridation technology, in order to suppress the threshold voltage shift of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). We find that supercritical NH<jats:sub>3</jats:sub> fluid has the characteristics of both liquid NH<jats:sub>3</jats:sub> and gaseous NH<jats:sub>3</jats:sub> simultaneously, i.e., high penetration and high solubility, which penetrate the packaging of MIS-HEMTs. In addition, <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{NH}}}_{2}^{-}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">NH</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_37_9_097101_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> produced via the auto coupling ionization of NH<jats:sub>3</jats:sub> has strong nucleophilic ability, and is able to fill nitrogen vacancies near the GaN surface created by high temperature processes. After supercritical fluid treatment, the threshold voltage shift is reduced from 1 V to 0 V, and the interface trap density is reduced by two orders of magnitude. The results show that the threshold voltage shift of MIS-HEMTs can be effectively suppressed by means of supercritical nitridation technology.</jats:p>

<jats:p>Transparent conducting materials (TCMs) have been widely used in optoelectronic applications such as touchscreens, flat panel displays and thin film solar cells. These applications of TCMs are currently dominated by n-type doped oxides. High-performance p-type TCMs are still lacking due to their low hole mobility or p-type doping bottleneck, which impedes efficient device design and novel applications such as transparent electronics. Here, based on first-principles calculations, we propose chalcogenide perovskite YScS<jats:sub>3</jats:sub> as a promising p-type TCM. According to our calculations, its optical absorption onset is above 3 eV, which allows transparency to visible light. Its hole conductivity effective mass is 0.48<jats:italic>m</jats:italic> <jats:sub>0</jats:sub>, which is among the smallest in p-type TCMs, suggesting enhanced hole mobility. It could be doped to p-type by group-II elements on cation sites, all of which yield shallow acceptors. Combining these properties, YScS<jats:sub>3</jats:sub> holds great promise to enhancing the performance of p-type TCMs toward their n-type counterparts.</jats:p>

<jats:p>We examine quantum anomalous Hall (QAH) insulators with intrinsic magnetism displaying quantized Hall conductance at zero magnetic fields. The spin-momentum locking of the topological edge stats promises QAH insulators with great potential in device applications in the field of spintronics. Here, we generalize Haldane’s model on the honeycomb lattice to a more realistic two-orbital case without the artificial real-space complex hopping. Instead, we introduce an intraorbital coupling, stemming directly from the local spin-orbit coupling (SOC). Our <jats:italic>d<jats:sub>xy</jats:sub> </jats:italic>/<jats:italic>d</jats:italic> <jats:sub> <jats:italic>x</jats:italic> <jats:sup>2</jats:sup>–<jats:italic>y</jats:italic> <jats:sup>2</jats:sup> </jats:sub> model may be viewed as a generalization of the bismuthene <jats:italic>p<jats:sub>x</jats:sub> </jats:italic>/<jats:italic>p<jats:sub>y</jats:sub> </jats:italic>-model for correlated <jats:italic>d</jats:italic>-orbitals. It promises a large SOC gap, featuring a high operating temperature. This two-orbital model nicely explains the low-energy excitation and the topology of two-dimensional ferromagnetic iron-halogenides. Furthermore, we find that electronic correlations can drive the QAH states to a <jats:italic>c</jats:italic> = 0 phase, in which every band carries a nonzero Chern number. Our work not only provides a realistic QAH model, but also generalizes the nontrivial band topology to correlated orbitals, which demonstrates an exciting topological phase transition driven by Coulomb repulsions. Both the model and the material candidates provide excellent platforms for future study of the interplay between electronic correlations and nontrivial band topology.</jats:p>

<jats:p>We report superconductivity in a new ternary molybdenum pnictide Rb<jats:sub>2</jats:sub>Mo<jats:sub>3</jats:sub>As<jats:sub>3</jats:sub>, synthesized via the solid state reaction method. Powder x-ray diffraction analysis reveals a hexagonal crystal structure with space group <jats:inline-formula> <jats:tex-math> <?CDATA $P\bar{6}m2$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>P</mml:mi> <mml:mover accent="true"> <mml:mn>6</mml:mn> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> <mml:mi>m</mml:mi> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_37_9_097401_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (No. 187), and the refined lattice parameters are <jats:italic>a</jats:italic> = 10.431(5) Å, <jats:italic>c</jats:italic> = 4.460(4) Å. SEM images show rod-like grains with good ductility, confirming a quasi-one-dimensional (Q1D) structure. Electrical resistivity and dc magnetic susceptibility characterizations exhibit superconductivity with an onset of <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> = 10.5 K. The upper critical field of Rb<jats:sub>2</jats:sub>Mo<jats:sub>3</jats:sub>As<jats:sub>3</jats:sub> is estimated to be 28.2T at zero temperature, providing an evidence of possible unconventional superconductivity. Our recent discovery of MoAs-based superconductors above 10 K provides a unique platform for the study of exotic superconductivity in 4<jats:italic>d</jats:italic> electron systems with Q1D crystal structures.</jats:p>

<jats:p>Using the newly-developed solid ionic gating technique, we measure the electrical transport property of a thin-flake NbSe<jats:sub>2</jats:sub> superconductor (<jats:italic>T</jats:italic> <jats:italic>c</jats:italic> = 6.67 K) under continuous Li intercalation and electron doping. It is found that the charge-density-wave transition is suppressed, while at the same time a carrier density, decreasing from 7 × 10<jats:sup>14</jats:sup> cm<jats:sup>–2</jats:sup> to 2 × 10<jats:sup>14</jats:sup> cm<jats:sup>–2</jats:sup> also occurs. This tunable capability in relation to carrier density is 70%, which is 5 times larger than that found using the liquid ionic gating method [Phys. Rev. Lett. 117 (2016) 106801]. Meanwhile, we find that the scattering type of conduction electrons transits to the <jats:italic>s</jats:italic>–<jats:italic>d</jats:italic> process, which may be caused by the change of the occupied states of 4<jats:italic>d</jats:italic>-electrons in Nb under the condition of Li intercalation. Simultaneously, we observe a certain decrement of electron-phonon coupling (EPC), based on the electron-phonon scattering model, in the high temperature range. Based on data gathered from <jats:italic>in situ</jats:italic> measurements, we construct a full phase diagram of carrier density, EPC and <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> in the intercalated NbSe<jats:sub>2</jats:sub> sample, and qualitatively explain the variation of <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> within the BCS framework. It is our opinion that the <jats:italic>in situ</jats:italic> solid ionic gating method provides a direct route to describing the relationship between carrier density and superconductivity, which is helpful in promoting a clearer understanding of electronic phase competition in transition metal dichalcogenides.</jats:p>

<jats:p>We develop an experimental tool to investigate the order parameter of superconductors by combining point-contact spectroscopy measurement with high-pressure technique. It is demonstrated for the first time that planar point-contact spectroscopy measurement on noncentrosymmetric superconducting PbTaSe<jats:sub>2</jats:sub> single crystals is systematically subjected to hydrostatic pressures up to 12.1 kbar. Under such a high pressure, the normal-state contact resistance is sensitive to the applied pressure, reflecting the underlying variation of contact transparency upon pressures. In a superconducting state, the pressure dependence of the energy gap <jats:italic>Δ</jats:italic> <jats:sub>0</jats:sub> and the critical temperature <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> for gap opening/closing are extracted based on a generalized Blond–Tinkham–Klapwijk model. The gap ratio 2<jats:italic>Δ</jats:italic> <jats:sub>0</jats:sub>/<jats:italic>k</jats:italic> <jats:sub>B</jats:sub> <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> indicates a crossover from weak coupling to strong coupling in electron pairing strength upon pressure for PbTaSe<jats:sub>2</jats:sub>. Our experimental results show the accessibility and validity of high-pressure point-contact spectroscopy, offering rich information about high-pressure superconductivity.</jats:p>

<jats:p>The Mott transition is one of the fundamental issues in condensed matter physics, especially in the system with antiferromagnetic long-range order. However, such a transition is rare in quantum spin liquid (QSL) systems without long-range order. Here we report the experimental pressure-induced insulator to metal transition followed by the emergence of superconductivity in the QSL candidate NaYbSe<jats:sub>2</jats:sub> with a triangular lattice of 4<jats:italic>f</jats:italic> Yb<jats:sup>3+</jats:sup> ions. Detail analysis of transport properties in metallic state shows an evolution from non-Fermi liquid to Fermi liquid behavior when approaching the vicinity of superconductivity. An irreversible structure phase transition occurs around 11 GPa, which is revealed by the x-ray diffraction. These results shed light on the Mott transition in the QSL systems.</jats:p>

<jats:p>In this work, we present a new mechanism for designing phase-gradient metasurfaces (PGMs) to control an electromagnetic wavefront with high efficiency. Specifically, we design a transmission-type PGM, formed by a periodic subwavelength metallic slit array filled with identical dielectrics of different heights. It is found that when Fabry–Pérot (FP) resonances occur locally inside the dielectric regions, in addition to the common phenomenon of complete transmission, the transmitted phase differences between two adjacent slits are exactly the same, being a nonzero constant. These local FP resonances ensure total phase shift across a supercell, fully covering a range of 0 to 2<jats:italic>π</jats:italic>, satisfying the design requirements of PGMs. Further research reveals that, due to local FP resonances, there is a one-to-one correspondence between the phase difference and the permittivity of the filled dielectric. A similar approach can be extended to the reflection-type case and other wavefront transformations, creating new opportunities for wave manipulation.</jats:p>

<jats:p>Distinctive superconducting behaviors between bulk and monolayer FeSe make it challenging to obtain a unified picture of all FeSe-based superconductors. We investigate the ultrafast quasiparticle (QP) dynamics of an intercalated superconductor (Li<jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub>Fe<jats:sub> <jats:italic>x</jats:italic> </jats:sub>)OHFe<jats:sub>1 – <jats:italic>y</jats:italic> </jats:sub>Se, which is a bulk crystal but shares a similar electronic structure with single-layer FeSe on SrTiO<jats:sub>3</jats:sub>. We obtain the electron-phonon coupling (EPC) constant <jats:italic>λ</jats:italic> <jats:sub> <jats:italic>A</jats:italic> <jats:sub>1g</jats:sub> </jats:sub> (0.22 ± 0.04), which well bridges that of bulk FeSe crystal and single-layer FeSe on SrTiO<jats:sub>3</jats:sub>. Significantly, we find that such a positive correlation between <jats:italic>λ</jats:italic> <jats:sub> <jats:italic>A</jats:italic> <jats:sub>1g</jats:sub> </jats:sub> and superconducting <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> holds among all known FeSe-based superconductors, even in line with reported FeAs-based superconductors. Our observation indicates possible universal role of EPC in the superconductivity of all known categories of iron-based superconductors, which is a critical step towards achieving a unified superconducting mechanism for all iron-based superconductors.</jats:p>