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<jats:p>We report a tunable transverse magnetoresistance of the planar Hall effect (PHE), up to 48% in the Ni<jats:sub>80</jats:sub>Fe<jats:sub>20</jats:sub>/HfO<jats:sub>2</jats:sub> heterostructures. This control is achieved by applying a gate voltage with an ionic liquid technique at ultra-low voltage, which exhibits a gate-dependent PHE. Moreover, in the range of 0-V to 1-V gate voltage, transverse magnetoresistance of PHE can be continuously regulated. Ferromagnetic resonance (FMR) also demonstrates the shift of the resonance field at low gate voltage. This provides a new method for the design of the electric field continuous control spintronics device with ultra-low energy consumption.</jats:p>

<jats:p>In this study, truncated octahedron (TO) structure is selected for further analysis and we focus on 38-atom Pd–Pt–Ag trimetallic nanoalloys. The best chemical ordering structures of Pd<jats:sub> <jats:italic>n</jats:italic> </jats:sub>Ag<jats:sub>32 – <jats:italic>n</jats:italic> </jats:sub>Pt<jats:sub>6</jats:sub> trimetallic nanoalloys are obtained at Gupta level. The structures with the lowest energy at Gupta level are then re-optimized by density functional theory (DFT) relaxations and DFT results confirm the Gupta level calculations with small shifts on bond lengths indicating TO structure is favorable for 38-atom of Pd<jats:sub> <jats:italic>n</jats:italic> </jats:sub>Ag<jats:sub>32 – <jats:italic>n</jats:italic> </jats:sub>Pt<jats:sub>6</jats:sub> trimetallic nanoalloys. The DFT excess energy analysis shows that Pd<jats:sub>8</jats:sub>Ag<jats:sub>24</jats:sub>Pt<jats:sub>6</jats:sub> composition has the lowest excess energy value in common with excess energy analysis at Gupta level. In Pd<jats:sub>8</jats:sub>Ag<jats:sub>24</jats:sub>Pt<jats:sub>6</jats:sub> composition, eight Pd atoms are central sites of 8 (111) hexagonal facets of TO, 24 Ag atoms locate on surface, and 6 Pt atoms locate at the core of the structure. It is also obtained that all of the compositions except Pd<jats:sub>18</jats:sub>Ag<jats:sub>14</jats:sub>Pt<jats:sub>6</jats:sub> and Pd<jats:sub>20</jats:sub>Ag<jats:sub>12</jats:sub>Pt<jats:sub>6</jats:sub> exhibit a octahedral Pt core. Besides, it is observed that there is a clear tendency for Ag atoms to segregate to the surface and also Pt atoms prefer to locate at core due to order parameter (<jats:italic>R</jats:italic>) variations.</jats:p>

<jats:p>Prototypical three-dimensional (3D) topological Dirac semimetals (DSMs), such as Cd<jats:sub>3</jats:sub>As<jats:sub>2</jats:sub> and Na<jats:sub>3</jats:sub>Bi, contain electrons that obey a linear momentum–energy dispersion with different Fermi velocities along the three orthogonal momentum dimensions. Despite being extensively studied in recent years, the inherent Fermi velocity anisotropy has often been neglected in the theoretical and numerical studies of 3D DSMs. Although this omission does not qualitatively alter the physics of light-driven massless quasiparticles in 3D DSMs, it does quantitatively change the optical coefficients which can lead to nontrivial implications in terms of nanophotonics and plasmonics applications. Here we study the linear optical response of 3D DSMs for general Fermi velocity values along each direction. Although the signature conductivity-frequency scaling, <jats:italic>σ</jats:italic>(<jats:italic>ω</jats:italic>) ∝ <jats:italic>ω</jats:italic>, of 3D Dirac fermion is well-protected from the Fermi velocity anisotropy, the linear optical response exhibits strong linear dichroism as captured by the universal extinction ratio scaling law, <jats:italic>Λ<jats:sub>ij</jats:sub> </jats:italic> = (<jats:italic>v<jats:sub>i</jats:sub> </jats:italic>/<jats:italic>v<jats:sub>j</jats:sub> </jats:italic>)<jats:sup>2</jats:sup> (where <jats:italic>i</jats:italic> ≠ <jats:italic>j</jats:italic> denotes the three spatial coordinates <jats:italic>x</jats:italic>,<jats:italic>y</jats:italic>,<jats:italic>z</jats:italic>, and <jats:italic>v<jats:sub>i</jats:sub> </jats:italic> is the <jats:italic>i</jats:italic>-direction Fermi velocity), which is independent of frequency, temperature, doping, and carrier scattering lifetime. For Cd<jats:sub>3</jats:sub>As<jats:sub>2</jats:sub> and Na<jats:sub>3</jats:sub>Bi<jats:sub>3</jats:sub>, an exceptionally strong extinction ratio larger than 15 and covering a broad terahertz window is revealed. Our findings shed new light on the role of Fermi velocity anisotropy in the optical response of Dirac semimetals and open up novel polarization-sensitive functionalities, such as photodetection and light modulation.</jats:p>

<jats:p>Graphene has been recognized as a promising candidate in developing tunable terahertz (THz) functional devices due to its excellent optical and electronic properties, such as high carrier mobility and tunable conductivity. Here, we review graphene-based THz modulators we have recently developed. First, the optical properties of graphene are discussed. Then, graphene THz modulators realized by different methods, such as gate voltage, optical pump, and nonlinear response of graphene are presented. Finally, challenges and prospective of graphene THz modulators are also discussed.</jats:p>

<jats:p>THz time-domain spectroscopy (THz-TDS) is used to study the THz-optical properties of a single crystal bismuth ferrite BiFeO<jats:sub>3</jats:sub> (BFO). It can be found that the anisotropy of BiFeO<jats:sub>3</jats:sub> is strongly dependent on the temperature. A giant birefringence up to around 3.6 is observed at 1 THz. The presence of a spatially modulated cycloidal antiferromagnetic structure leads to spin cycloid resonances (SCR) <jats:italic>ψ</jats:italic> and <jats:italic>Φ</jats:italic>, corresponding to the out-of-plane and in-plane modes of the spin cycloid, respectively. We distinguish the SCR with respect to their response to orthogonal polarizations of the electric fields of the incident THz beam. In addition, we observe a resonance appearing below 140 K, which might be interpreted as an electromagnon mode and related to a spin reorientation transition. Our present observations present that the temperature and polarization, as the external control parameters, can be used to modulate the THz optical properties of BFO single crystal.</jats:p>

<jats:p>To elucidate the regulation mechanism of catalyst geometry structure to diamond growth, we establish three catalyst modes with different structures. The simulation results show that with the decrease of the protruding height of the catalyst, the low-temperature region gradually moves toward the center of the catalyst, which causes the distribution characteristics of the temperature and convection field in the catalyst to change. The temperature difference in vertical direction of the catalyst decreases gradually and increases in the horizontal direction, while the catalyst convection velocity has the same variation regularity in the corresponding directions. The variation of temperature difference and convection velocity lead the crystal growth rate in different crystal orientations to change, which directly affects the crystal morphology of the synthetic diamond. The simulation results are consistent with the experimental results, which shows the correctness of the theoretical rational analysis. This work is expected to be able to facilitate the understanding of catalyst structure regulation mechanism on diamond morphology and the providing of an important theoretical basis for the controllable growth of special crystal shape diamond under HPHT process.</jats:p>

<jats:p>The site occupancy behavior of ternary alloying elements in <jats:italic>γ</jats:italic>′-Ni<jats:sub>3</jats:sub>Al (a key strengthening phase of commercial Ni-based single-crystal superalloys) can change with temperature and alloy composition owing to the effect of entropy. Using a total-energy method based on density functional theory, the dependence of tensile and shear behaviors on the site preference of alloying elements in <jats:italic>γ</jats:italic>′-Ni<jats:sub>3</jats:sub>Al were investigated in detail. Our results demonstrate that Fe, Ru, and Ir can significantly improve the ideal tensile and shear strength of the <jats:italic>γ</jats:italic>′ phase when occupying the Al site, with Ru resulting in the strongest enhancement. In contrast, elements with fully filled d orbitals (<jats:italic>i.e.</jats:italic>, Cu, Zn, Ag, and Cd) are expected to reduce the ideal tensile and shear strength. The calculated stress–strain relationships of Ni<jats:sub>3</jats:sub>Al alloys indicate that none of the alloying elements can simultaneously increase the ideal strength of the <jats:italic>γ</jats:italic>′ phase for both Ni1-site and Ni2-site substitutions. In addition, the charge redistribution and the bond length of the alloying elements and host atoms during the tensile and shear processes are analyzed to unveil the underlying electronic mechanisms.</jats:p>

<jats:p>Microtubule self-organization under mechanical and chemical regulations plays a central role in cytokinesis and cellular transportations. In plant-cells, the patterns or phases of cortical microtubules organizations are the direct indicators of cell-phases. The dense nematic pattern of cortical microtubule array relies on the regulation of single microtubule dynamics with mechanical coupling to steric interaction among the self-organized microtubule crowds. Building upon previous minimal models, we investigate the effective microtubule width, microtubule catastrophe rate, and zippering angle as factors that regulate the self-organization of the dense nematic phase. We find that by incorporating the effective microtubule width, the transition from isotropic to the highly ordered nematic phase (<jats:italic>N</jats:italic> <jats:sub>I</jats:sub> phase) with extremely long microtubules will be gapped by another nematic phase which consists of relative short microtubules (<jats:italic>N</jats:italic> <jats:sub>II</jats:sub> phase). The <jats:italic>N</jats:italic> <jats:sub>II</jats:sub> phase in the gap grows wider with the increase of the microtubule width. We further illustrate that in the dense phase, the collision-induced catastrophe rate and an optimal zippering angle play an important role in controlling the order–disorder transition, as a result of the coupling between the collision events and ordering. Our study shows that the transition to dense microtubule array requires the cross-talk between single microtubule growth and mechanical interactions among microtubules in the active crowds.</jats:p>

<jats:p>The use of single walled carbon nanotube-based nanoelectromechanical system (NEMS) resonator to sense the biomolecules’ mass is investigated under the influence of an external ac-field. A single walled carbon nanotube (SWCNT) cantilever has been proposed and studied if the mass is attached at the tip or various intermediate positions. The shift of the resonant frequency and the quality factor have been investigated and show high sensitivity to the attached mass of biomolecule and its position. The proposed SWCNT-based NEMS resonator is a good candidate for sensing and tracing biomolecules’ mass as concentration of acetone in human exhale, resulting in a painless, correct, and simple diabetics’ diagnosis.</jats:p>

<jats:p>Photodetectors based on amorphous InGaZnO (a-IGZO) thin film transistor (TFT) and halide perovskites have attracted attention in recent years. However, such a stack assembly of a halide perovskite layer/an a-IGZO channel, even with an organic semiconductor film inserted between them, easily has a very limited photoresponsivity. In this article, we investigate photoresponsive characteristics of TFTs by using CsPb<jats:italic>X</jats:italic> <jats:sub>3</jats:sub> (<jats:italic>X</jats:italic> = Br or I) quantum dots (QDs) embedded into the a-IGZO channel, and attain a high photoresponsivity over 10<jats:sup>3</jats:sup>A⋅W<jats:sup>−1</jats:sup>, an excellent detectivity in the order of 10<jats:sup>16</jats:sup> Jones, and a light-to-dark current ratio up to 10<jats:sup>5</jats:sup> under visible lights. This should be mainly attributed to the improved transfer efficiency of photoelectrons from the QDs to the a-IGZO channel. Moreover, spectrally selective photodetection is demonstrated by introducing halide perovskite QDs with different bandgaps. Thus, this work provides a novel strategy of device structure optimization for significantly improving the photoresponsive characteristics of TFT photodetectors.</jats:p>