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<jats:p>Two-dimensional (2D) semiconducting tin disulfide (SnS<jats:sub>2</jats:sub>) has been widely used for optoelectronic applications. To functionalize SnS<jats:sub>2</jats:sub> for extending its application, we investigate the stability, electronic and magnetic properties of substitutional doping by high throughput first-principles calculations. There are a lot of elements that can be doped in monolayer SnS<jats:sub>2</jats:sub>. Nonmetal in group A can introduce p-type and n-type carriers, while most metals in group A can only lead to p-type doping. Not only 3d, but also 4d and 5d transition metals in groups VB to VIIIB9 can introduce magnetism in SnS<jats:sub>2</jats:sub>, which is potentially applicable for spintronics. This study provides a comprehensive view of functionalization of SnS<jats:sub>2</jats:sub> by substitutional doping, which will guide further experimental realization.</jats:p>

<jats:p>The first-principles calculations were used to explore the tunable electronic structure in DyNiO<jats:sub>3</jats:sub> (DNO) under the effects of the biaxial compressive and tensile strains. We explored how the biaxial strain tunes theorbital hybridization and influences the charge and orbital ordering states. We found that breathing mode and Jahn–Teller distortion play a primary role in charge ordering state and orbital ordering state, respectively. Additionally, the calculated results revealed that the biaxial strain has the ability to manipulate the phase competition between the two states. A phase transition point has been found under tensile train. If the biaxial train is larger than the point, the system favors orbital ordering state. If the strain is smaller than the point, the system is in charge ordering state favorably.</jats:p>

<jats:p>We investigate the electronic structure and magnetic properties of layered compound Sr<jats:sub>3</jats:sub>Fe<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> based on first-principles calculations in the framework of density functional theory with GGA+<jats:italic>U</jats:italic> method. Under high pressure, the ladder-type layered structure of Sr<jats:sub>3</jats:sub>Fe<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> is transformed into the infinite layered structure accompanied by a transition from G-type anti-ferromagnetic (AFM) insulator to ferromagnetic (FM) metal and a spin transition from <jats:italic>S</jats:italic> = 2 to <jats:italic>S</jats:italic> = 1. We reproduce these transformations in our calculations and give a clear physical interpretation.</jats:p>

<jats:p>As an ultrasensitive sensing technology, the application of surface enhanced Raman spectroscopy (SERS) is one interesting topic of nano-optics, which has huge application prospectives in plenty of research fields. In recent years, the bottleneck in SERS application could be the fabrication of SERS substrate with excellent enhancement. In this work, a two-dimensional (2D) Ag nanorice film is fabricated by self-assembly method as a SERS substrate. The collected SERS spectra of various molecules on this 2D plasmonic film demonstrate quantitative detection could be performed on this SERS substrate. The experiment data also demonstrate this 2D plasmonic film consisted of anisotropic nanostructures has no obvious SERS polarization dependence. The simulated electric field distribution points out the SERS enhancement comes from the surface plasmon coupling between nanorices. And the SERS signals is dominated by molecules adsorbed at different regions of nanorice surface at various wavelengths, which could be a good near IR SERS substrate for bioanalysis. Our work not only enlarges the surface plasmon properties of metal nanostructure, but also exhibits the good application prospect in SERS related fields.</jats:p>

<jats:p>Alpha particle radiation detectors with planar double Schottky contacts (DSC) are directly fabricated on 5-μm-thick epitaxial semi-insulating (SI) GaN:Fe film with resistivity higher than 1 × 10<jats:sup>8</jats:sup> Ω ⋅cm. Under 10 V bias, the detector exhibits a low dark current of less than 5.0 × 10<jats:sup>−11</jats:sup> A at room-temperature, which increases at higher temperatures. Linear behavior in the semi-log reverse current–voltage plot suggests that Poole–Frenkel emission is the dominant carrier leakage mechanism at high bias. Distinct double-peak characteristics are observed in the energy spectrum of alpha particles regardless of bias voltage. The energy resolution of the SI-GaN based detector is determined to be ∼ 8.6% at the deposited energy of 1.209 MeV with a charge collection efficiency of ∼ 81.7%. At a higher temperature of 90 °C, the measured full width at half maximum (FWHM) rises to 235 keV with no shift of energy peak position, which proves that the GaN detector has potential to work stably in high temperature environment. This study provides a possible route to fabricate the low cost GaN-based alpha particle detector with reasonable performance.</jats:p>

<jats:p>The successfully experimental fabrication of two-dimensional Te monolayer films [<jats:italic>Phys. Rev. Lett.</jats:italic> <jats:bold>119</jats:bold> 106101 (2017)] has promoted the researches on the group-VI monolayer materials. In this work, the electronic structures and topological properties of a group-VI binary compound of TeSe<jats:sub>2</jats:sub> monolayers are studied based on the density functional theory and Wannier function method. Three types of structures, namely, <jats:italic>α</jats:italic>-TeSe<jats:sub>2</jats:sub>, <jats:italic>β</jats:italic>-TeSe<jats:sub>2</jats:sub>, and <jats:italic>γ</jats:italic>-TeSe<jats:sub>2</jats:sub>, are proposed for the TeSe<jats:sub>2</jats:sub> monolayer among which the <jats:italic>α</jats:italic>-TeSe<jats:sub>2</jats:sub> is found being the most stable. All the three structures are semiconductors with indirect band gaps. Very interestingly, the <jats:italic>γ</jats:italic>-TeSe<jats:sub>2</jats:sub> monolayer becomes a quantum spin Hall (QSH) insulator with a global nontrivial energy gap of 0.14 eV when a 3.5% compressive strain is applied. The opening of the global band gap is understood by the competition between the decrease of the local band dispersion and the weakening of the interactions between the Se p<jats:sub> <jats:italic>x</jats:italic> </jats:sub>, p<jats:sub> <jats:italic>y</jats:italic> </jats:sub> orbitals and Te p<jats:sub> <jats:italic>x</jats:italic> </jats:sub>, p<jats:sub> <jats:italic>y</jats:italic> </jats:sub> orbitals during the process. Our work realizes topological states in the group-VI monolayers and promotes the potential applications of the materials in spintronics and quantum computations.</jats:p>

<jats:p>A magnetic field-controlled spin-current diode is theoretically proposed, which consists of a junction with an interacting quantum dot sandwiched between a pair of nonmagnetic electrodes. By applying a spin bias <jats:italic>V</jats:italic> <jats:sub>S</jats:sub> across the junction, a pure spin current can be obtained in a certain gate voltage regime,regardless of whether the Coulomb repulsion energy exists. More interestingly, if we applied an external magnetic field on the quantum dot, we observed a clear asymmetry in the spectrum of spin current <jats:italic>I</jats:italic> <jats:sub>S</jats:sub> as a function of spin bias, while the charge current always decays to zero in the Coulomb blockade regime. Such asymmetry in the current profile suggests a spin diode-like behavior with respect to the spin bias, while the net charge through the device is almost zero. Different from the traditional charge current diode, this design can change the polarity direction and rectifying ability by adjusting the external magnetic field, which is very convenient. This device scheme can be compatible with current technologies and has potential applications in spintronics or quantum processing.</jats:p>

<jats:p>For photon detection, superconducting transition-edge sensor (TES) micro-calorimeters are excellent energy-resolving devices. In this study, we report our recent work in developing Ti-/Au-based TES. The Ti/Au TES devices were designed and implemented with a thickness ratio of 1:1 and different suspended structures using micromachining technology. The characteristics were evaluated and analyzed, including surface morphology, 3D deformation of suspended Ti/Au TES device structure, <jats:italic>I</jats:italic>–<jats:italic>V</jats:italic> characteristics, and low-temperature superconductivity. The results showed that the surface of Ti/Au has good homogeneity and the surface roughness of Ti/Au is significantly increased compared with the substrate. The structure of Ti/Au bilayer film significantly affects the deformation of suspended devices, but the deformation does not affect the <jats:italic>I</jats:italic>–<jats:italic>V</jats:italic> characteristics of the devices. For devices with the Ti/Au bilayer (150 – m × 150 μm) and beams (100 μ m × 25 μm), the transition temperature (<jats:italic>T</jats:italic> <jats:sub>c</jats:sub>) is 253 mK with a width of 6 mK, and the value of the temperature sensitivity <jats:italic>α</jats:italic> is 95.1.</jats:p>

<jats:p>We study the possibility to realize a Majorana zero mode that is robust and may be easily manipulated for braiding in quantum computing in the ground state of the Kitaev model in this work. To achieve this we first apply a uniform [111] magnetic field to the gapless Kitaev model and turn the Kitaev model to an effective p + ip topological superconductor of spinons. We then study possible vortex binding in such system to a topologically trivial spot in the ground state. We consider two cases in the system: one is a vacancy and the other is a fully polarized spin. We show that in both cases, the system binds a vortex with the defect and a robust Majorana zero mode in the ground state at a weak uniform [111] magnetic field. The distribution and asymptotic behavior of these Majorana zero modes are studied. The Majorana zero modes in both cases decay exponentially in space, and are robust against local perturbations and other Majorana zero modes far away, which makes them promising candidates for braiding in topological quantum computing.</jats:p>

<jats:p>Two-dimensional ferromagnetic van der Waals (2D vdW) heterostructures have opened new avenues for creating artificial materials with unprecedented electrical and optical functions beyond the reach of isolated 2D atomic layered materials, and for manipulating spin degree of freedom at the limit of few atomic layers, which empower next-generation spintronic and memory devices. However, to date, the electronic properties of 2D ferromagnetic heterostructures still remain elusive. Here, we report an unambiguous magnetoresistance behavior in CrI<jats:sub>3</jats:sub>/graphene heterostructures, with a maximum magnetoresistance ratio of 2.8%. The magnetoresistance increases with increasing magnetic field, which leads to decreasing carrier densities through Lorentz force, and decreases with the increase of the bias voltage. This work highlights the feasibilities of applying two-dimensional ferromagnetic vdW heterostructures in spintronic and memory devices.</jats:p>