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<jats:p>The group-V monolayers (MLs) have been studied intensively after the experimental fabrication of two-dimensional (2D) graphene and black phosphorus. The observation of novel quantum phenomena, such as quantum spin Hall effect and ferroelectricity in group-V elemental layers, has attracted tremendous attention because of the novel physics and promising applications for nanoelectronics in the 2D limit. In this review, we comprehensively review recent research progress in engineering of topology and ferroelectricity, and several effective methods to control the quantum phase transition are discussed. We then introduce the coupling between topological orders and ferroelectric orders. The research directions and outlooks are discussed at the end of the perspective. It is expected that the comprehensive overview of topology and ferroelectricity in 2D group-V materials can provide guidelines for researchers in the area and inspire further explorations of interplay between multiple quantum phenomena in low-dimensional systems.</jats:p>

<jats:p>We study the dynamics of the entropic uncertainty for three types of three-level atomic systems coupled to an environment modeled by random matrices. The results show that the entropic uncertainty in the Ξ-type atomic system is lower than that in the V-type atomic system which is exactly the same as that in the Λ-type atomic system. In addition, the effect of relative coupling strength on entropic uncertainty is opposite in Markov region and non-Markov region, and the influence of a common environment and independent environments in Markov region and non-Markov region is also opposite. One can reduce the entropic uncertainty by decreasing relative coupling strength or placing the system in two separate environments in the Markov case. In the non-Markov case, the entropic uncertainty can be reduced by increasing the relative coupling strength or by placing the system in a common environment.</jats:p>

<jats:p>The excellent reverse breakdown characteristics of Schottky barrier varactor (SBV) are crucially required for the application of high power and high efficiency multipliers. The SBV with a novel Schottky structure named metal–brim is fabricated and systemically evaluated. Compared with normal structure, the reverse breakdown voltage of the new type SBV improves from –7.31 V to –8.75 V. The simulation of the Schottky metal–brim SBV is also proposed. Three factors, namely distribution of leakage current, the electric field, and the area of space charge region are mostly concerned to explain the physical mechanism. Schottky metal–brim structure is a promising approach to improve the reverse breakdown voltage and reduce leakage current by eliminating the accumulation of charge at Schottky electrode edge.</jats:p>

<jats:p>A high performance InAlN/GaN high electron mobility transistor (HEMT) at low voltage operation (6–10 V drain voltage) has been fabricated. An 8 nm InAlN barrier layer is adopted to generate large 2DEG density thus to reduce sheet resistance. Highly scaled lateral dimension (1.2 μm source–drain spacing) is to reduce access resistance. Both low sheet resistance of the InAlN/GaN structure and scaled lateral dimension contribute to an high extrinsic transconductance of 550 mS/mm and a large drain current of 2.3 A/mm with low on-resistance (<jats:italic>R</jats:italic> <jats:sub>on</jats:sub>) of 0.9 Ω⋅mm. Small signal measurement shows an <jats:italic>f</jats:italic> <jats:sub>T</jats:sub>/<jats:italic>f</jats:italic> <jats:sub>max</jats:sub> of 131 GHz/196 GHz. Large signal measurement shows that the InAlN/GaN HEMT can yield 64.7%–52.7% (<jats:italic>V</jats:italic> <jats:sub>ds</jats:sub> = 6–10 V) power added efficiency (PAE) associated with 1.6–2.4 W/mm output power density at 8 GHz. These results demonstrate that GaN-based HEMTs not only have advantages in the existing high voltage power and high frequency rf field, but also are attractive for low voltage mobile compatible rf applications.</jats:p>

<jats:p>The luminescence intensity regulation of organic light-emitting transistor (OLED) device can be achieved effectively by the combination of graphene vertical field effect transistor (GVFET) and OLED. In this paper, we fabricate and characterize the graphene vertical field-effect transistor with gate dielectric of ion–gel film, confirming that its current switching ratio reaches up to 10<jats:sup>2</jats:sup>. Because of the property of high light transmittance in ion–gel film, the OLED device prepared with graphene/PEDOT:PSS as composite anode exhibits good optical properties. We also prepare the graphene vertical organic light-emitting field effect transistor (GVOLEFET) by the combination of GVFET and graphene OLED, analyzing its electrical and optical properties, and confirming that the luminescence intensity can be significantly changed by regulating the gate voltage.</jats:p>

<jats:p>The Nd–Fe–B magnets are pre-sintered and then processed with hot-pressing, and the resulting magnets are called the hot-pressed pretreated (HPP) magnets. The coercivity of the HPP magnets increases as the annealed temperature increases. When the annealing temperature is 900 °C, the coercivity of the magnet is only 17.6 kOe (1 Oe = 79.5775 A⋅m<jats:sup>–1</jats:sup>), but when the annealing temperature rises up to 1060 °C, the coercivity of the magnet reaches 23.53 kOe, which is remarkably increased by 33.7%. The microstructure analysis indicates that the grain surface of the HPP magnet becomes smoother as the annealed temperature increases. The microstructure factor <jats:italic>α</jats:italic> is changed according to the intrinsic coercivity model formula. The <jats:italic>α</jats:italic> of the magnet at 900 °C is only 0.578, but it is 0.825 at 1060 °C. Microstructural optimization is due mainly to the increase of coercivity of the HPP magnet.</jats:p>

<jats:p>As a prototypical transition-metal dichalcogenide semiconductor, MoS<jats:sub>2</jats:sub> possesses strong spin–orbit coupling, which provides an ideal platform for the realization of interesting physical phenomena. Here, we report the magnetotransport properties in NbN–MoS<jats:sub>2</jats:sub>–NbN sandwich junctions at low temperatures. Above the critical temperature around ∼11 K, the junction resistance shows weak temperature dependence, indicating a tunneling behavior. While below ∼11 K, nearly zero junction resistance is observed, indicating the superconducting state in the MoS<jats:sub>2</jats:sub> layer induced by the superconducting proximity effect. When a perpendicular magnetic field ∼1 T is applied, such proximity effect is suppressed, accompanying with insulator-like temperature-dependence of the junction resistance. Intriguingly, when further increasing the magnetic field, the junction conductance is significantly enhanced, which is related to the enhanced single particle tunneling induced by the decrease of the superconducting energy gap with increasing magnetic fields. In addition, the possible Majorana zero mode on the surface of MoS<jats:sub>2</jats:sub> can further lead to the enhancement of the junction conductance.</jats:p>

<jats:p>The magnetic phase diagram of rare-earth perovskite compound, GdScO<jats:sub>3</jats:sub>, has been investigated by magnetization and heat capacity. The system undergoes an antiferromagnetic phase transition at <jats:italic>T</jats:italic> <jats:sub>N</jats:sub> = 2.6 K, with an easy axis of magnetization along the <jats:italic>a</jats:italic> axis. The magnetization measurements show that it exists a spin-flop transition around 0.3 T for the applied field along the <jats:italic>a</jats:italic> axis. The critical magnetic field for the antiferromagnetic-to-paramagnetic transition is near 3.2 T when temperature approaches zero. By scaling susceptibilities, we presume this point (<jats:italic>B</jats:italic> = 3.2 T, <jats:italic>T</jats:italic> = 0 K) might be a field-induced quantum critical point and the magnetic critical fluctuations can even be felt above <jats:italic>T</jats:italic> <jats:sub>N</jats:sub>.</jats:p>

<jats:p>Heavily Mn-doped SiGe thin films were grown by radio frequency magnetron sputtering and then treated by post-growth thermal annealing. Structural characterizations reveal the coexistence of Mn-diluted SiGe crystals and Mn-rich nanoclusters in the annealed films. Magnetic measurements indicate the ferromagnetic ordering of the annealed samples above room temperature . The data suggest that the ferromagnetism is probably mainly contributed by the Ge-rich nanoclusters and partially contributed by the tensile-strained Mn-diluted SiGe crystals. The results may be useful for room temperature spintronic applications based on group IV semiconductors.</jats:p>

<jats:p>In quasi-one-dimensional (q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic (AFM) compound YbAlO<jats:sub>3</jats:sub>, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations, and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave (LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.</jats:p>