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<jats:title>Abstract</jats:title> <jats:p>The Janus monolayer transition metal dichalcogenides (TMDs) MXY (M=Mo, W, etc. and X, Y=S, Se, etc.) have been successfully synthesized in recent years. The Rashba spin splitting in these compounds arises due to the breaking of out-of-plane mirror symmetry. Here we study the pairing symmetry of superconducting Janus monolayer TMDs within the weak-coupling framework near critical temperature T$_c$, of which the Fermi surface (FS) sheets centered around both $\Gamma$ and $K(K')$ points. We find that the strong Rashba splitting produces two kinds of topological superconducting states which differ from that in its parent compounds. More specifically, at relatively high chemical potentials, we obtain a time-reversal invariant $s + f + p$-wave mixed superconducting state, which is fully gapped and topologically nontrivial, i.e., a $\mathbb{Z}_2$ topological state. On the other hand, a time-reversal symmetry breaking $d + p + f$-wave superconducting state appears at lower chemical potentials. This state possess a large Chern number $|C|=6$ at appropriate pairing strength, demonstrating its nontrivial band topology. Our results suggest the Janus monolayer TMDs to be a promising candidate for the intrinsic helical and chiral topological superconductors.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>High-fidelity quantum logic gates are essential in quantum computation, and both photons and electron spins in quantum dots (QDs) have their own unique advantages in implementing quantum computation. It is of critical significance to achieve high-fidelity quantum gates for photon-QD hybrid systems. Here, we propose two schemes for implementing high-fidelity universal quantum gates including Toffoli gate and Fredkin gate for photon-QD hybrid systems, utilizing the practical scattering of a single photon off a QD-cavity system. The computation errors from the imperfections involved in the practical scattering are detected and prevented from arising in the final results of the two gates. Accordingly, the unity fidelity of each quantum gate is obtained in the nearly realistic condition, and the requirement for experimental realization is relaxed. Furthermore, the quantum circuits for the two gates are compact and no auxiliary qubits are required, which would be also the advantages regarding their experimental feasibility. These features indicate that our schemes may be useful in the practical quantum computation tasks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The flourishing rare earth superhydrides are a class of recently discovered materials that possess near-room-temperature superconductivity at high pressures, opening a new era of superconductivity research at high pressures. Among these superhydrides, yttrium superhydrides attracted great interest owing to their abundance of stoichiometries and excellent superconductivities. Here, we carried out a comprehensive study of yttrium superhydrides in a wide pressure range of 140-300 GPa. We successfully synthesized a series of superhydrides with the compositions of YH<jats:sub>4</jats:sub>, YH<jats:sub>6</jats:sub>, YH<jats:sub>7</jats:sub>, and YH<jats:sub>9</jats:sub>, and reported their superconducting transition temperatures of 82 K at 167 GPa, 218 K at 165 GPa, 29 K at 162 GPa, and 230 K at 300 GPa, respectively, which were evidenced by sharp drops of the resistance. The structure and superconductivity of YH<jats:sub>4</jats:sub>, which was taken as a representative example, were also examined by X-ray diffraction measurements and the suppression of the superconductivity under external magnetic fields, respectively. Clathrate YH<jats:sub>10</jats:sub> as a candidate of room-temperature superconductor was not synthesized within the studied pressure and temperature ranges of up to 300 GPa and 2000 K. The current work created a detailed platform for further searching room-temperature superconductors in polynary yttrium-based superhydrides.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The reverse gate leakage mechanism of W-gate and TiN-gate AlGaN/GaN HEMTs with N<jats:sub>2</jats:sub> plasma surface treatment is investigated by using current-voltage (I-V), capacitance-voltage (C-V) characteristics and theoretical calculation analysis. It is found that the main reverse gate leakage mechanism of both devices is the trap-assisted tunneling (TAT) mechanism at the entire reverse bias region (-30V - 0V). To the best of our knowledge, this is the first time that the analysis of the reverse gate leakage mechanism of W-gate AlGaN/GaN HEMTs has been studied. It is also found that the reverse gate leakage current of the W-gate AlGaN/GaN HEMTs is smaller than that of the TiN gate at high reverse gate bias voltage. Further, the activation energies of the extracted W-gate and TiN-gate AlGaN/GaN HEMTs are 0.0551eV-0.127eV and 0.112eV-0.201eV, respectively.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Strong ‘spin’-orbit coupled one-dimensional hole gas is achievable in a Ge nanowire in the presence of a strong magnetic field. The strong magnetic field lifts the two-fold degeneracy in the hole subband dispersions, such that the effective low-energy subband dispersion exhibits strong ‘spin’-orbit coupling. Here, we study the electrical ‘spin’ manipulation in a Ge nanowire quantum dot for both the lowest and second lowest hole subband dispersions. Using a finite square well to model the quantum dot confining potential, we calculate exactly the level splitting of the ‘spin’-orbit qubit and the Rabi frequency in the electric-dipole ‘spin’ resonance. The ‘spin’-orbit coupling modulated longitudinal <jats:italic>g</jats:italic>-factor <jats:italic>g</jats:italic> <jats:sub>so</jats:sub> is not only non-vanishing but also magnetic field dependent. Moreover, the ‘spin’-orbit couplings of the lowest and second lowest subband dispersions have opposite magnetic dependences, such that the results for these two subband dispersions are totally different.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We systematically investigate the influence of InSb interface (IF) engineering on the crystal quality and optical properties of strain-balanced InAs/GaSb type-II superlattices (T2SLs). The type II superlattice structure is 120 periods InAs (8 ML)/GaSb (6 ML) with different thicknesses of InSb interface grown by molecular beam epitaxy (MBE). The high-resolution X-ray diffraction (XRD) curves display the sharp satellite peaks, and the narrow full width at half maximum (FWHM) of the 0<jats:sup>th</jats:sup> are only 30-39 arcsecends. From the high-resolution cross-sectional transmission electron microscopy (HRTEM) characterization, the InSb heterointerfaces and the clear spatial separation between the InAs and GaSb layers can be more intuitively distinguished. As the InSb interface thickness increases, the compressive strain increases, and the surface "bright spots" appear to be more apparent from Atomic force microscopy (AFM) results. Also, photoluminescence (PL) measurements verifies that with the increase of the strain, the bandgap of the superlattice narrows. By optimizing the InSb interface, a high quality crystal with a well-defined surface and interface is obtained, with a PL wavelength of 4.78 um, which can be used for mid-wave infrared (MWIR) detection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Super-resolution imaging with superlens has been one of the fundamental research topics. Unfortunately, the resolution of superlens is inevitably restrained by material loss. To address the problem, we introduce the solid immersion mechanism into the slab superlens and the cylindrical superlens. The proposed solid immersion slab superlens (SISSL) and the solid immersion cylindrical superlens (SICSL) can improve resolution by converting evanescent wave to propagating wave using high refractive index materials. From the perspective of applications, the cylindrical superlens with finite cross section and the ability of magnification or demagnification has more advantages than slab superlens. Therefore, we focus on demonstrating analytically the super-resolution imaging of SICSL. Due to the impedance mismatching caused by solid immersion mechanism, the whispering gallery modes (WGMs) are excited between SICSL and the air interface. We clarify the excitation conditions of WGMs and analyze their influence on the imaging quality of SICSL. The SISSL and SICSL may pave a way to apply in lithography technique and real-time biomolecular imaging in future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Topological interface state (TIS) of elastic wave has attracted significant research interest due to its potential prospects in strengthening acoustic energy and enhancing the signal accuracy of damage identification and quantification. However, previous implementations on the interface modes of surface waves are limited to the non-adjustable frequency band and unalterable mode width. Here, we demonstrate the tunable TIS and topological resonance state (TRS) of Rayleigh wave by using a shape memory alloy (SMA) stubbed semi-infinite one-dimensional (1D) solid phononic crystals (PnCs), which simultaneously possesses the adjustable mode width. The mechanism of tunability stems from the phase transformation of the SMA between the martensite at low temperature and the austenite at high temperature. The tunable TIS of Rayleigh wave is realized by combining two bandgap-opened PnCs with different Zak phase. The TRS with adjustable mode width is achieved in the heterostructures by adding PnCs with Dirac point to the middle of two bandgap-opened PnCs with different Zak phase, which exhibits the extraordinary robustness in contrast to the ordinary Fabry-Pérot resonance state. This research provides new possibilities for the highly adjustable Rayleigh wave manipulation and find promising applications such as tunable energy harvesters, wide-mode filters and high-sensitivity Rayleigh wave detectors.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this study, a multiwavelength tunable ring-cavity erbium-doped fiber laser (EDFL) based on a Lyot filter was presented. For the proposed Lyot filter, a comb filter consisting of an EDF-polarization-maintaining fiber (EDF-PMF), a polarization controller (PC), and a circulator with four ports was used to suppress the mode competition. The light transmission direction was guaranteed by the circulator. For the proposed fiber laser, tunable single, dual, triple, quadruple, quintuple, sextuple, and septuple wavelengths were realized. A single-wavelength laser output with an optical signal-to-noise ratio (SNR) of up to 30.56 dB was realized, and a tuning range of 1590.54 to 1599.54 nm was achieved by tuning the PC. The stability of the single, dual, triple and quadruple-wavelength center power fluctuations was less than 0.05, 0.98, 5.07, and 7.71 dB respectively. When the laser was operated in the multiwavelength condition, the SNR was more than 20.97 dB. The proposed erbium-doped fiber laser is suitable for fiber-sensing system applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Cyclocarbon fully consists of <jats:italic>sp</jats:italic>-hybridized carbon atoms, which shows quite unusual electronic and geometric structures compared to common molecules. In this work, we systematically studied strain energy (SE) of cyclocarbons of different sizes using regression analysis method based on electronic energies evaluated at the very accurate DLPNO-CCSD(T)/cc-pVTZ theoretical level. In addition, ring strain of two systems closely related to cyclocarbon, boron nitride (BN) ring and cyclic polyacetylene (c-PA), is also explored. Very ideal relationships between SE and number of repeat units (<jats:italic>n</jats:italic>) are built for cyclo[2<jats:italic>n</jats:italic>]carbon, B<jats:sub> <jats:italic>n</jats:italic> </jats:sub>N<jats:sub> <jats:italic>n</jats:italic> </jats:sub>, and [2<jats:italic>n</jats:italic>]c-PA as SE = 555.0·<jats:italic>n</jats:italic> <jats:sup>-1</jats:sup>, 145.1·<jats:italic>n</jats:italic> <jats:sup>-1</jats:sup> and 629.8·<jats:italic>n</jats:italic> <jats:sup>-1</jats:sup> kcal·mol<jats:sup>-1</jats:sup>, respectively, and the underlying reasons of the difference and similarity in their SEs are discussed from electronic structure perspective. In addition, force constant of harmonic potential of C-C-C angles in cyclocarbon is derived based on SE values, the result is found to be 56.23 kcal·mol<jats:sup>-1</jats:sup>·rad<jats:sup>-2</jats:sup>. The possibility of constructing homodesmotic reactions to calculate SEs of cyclocarbons is also explored in this work, although this method is far less rigorous than the regression analysis method, its result is qualitatively correct has the advantage of much lower computational cost. In addition, comparison shows that ωB97XD/def2-TZVP is a good inexpensive alternative to the DLPNO-CCSD(T)/cc-pVTZ for evaluating energies used in deriving SE, while the popular and very cheap B3LYP/6-31G(d) level should be used with caution for systems with global electron conjugation such as c-PA.</jats:p>