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<jats:title>Abstract</jats:title> <jats:p>A highly reliable and selective ethanol gas sensor working in realistic environments based on alpha-Fe<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> (<jats:italic>α</jats:italic>-Fe<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>) nanorhombs is developed. The sensor is fabricated by integrating <jats:italic>α</jats:italic>-Fe<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> nanorhombs onto a low power microheater based on micro-electro-mechanical systems (MEMS) technology. The <jats:italic>α</jats:italic>-Fe<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> nanorhombs, prepared via a solvothermal method, is characterized by transmission electron microscopy (TEM), Raman spectroscopy, x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). The sensing performances of the <jats:italic>α</jats:italic>-Fe<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> sensor to various toxic gases are investigated. The optimum sensing temperature is found to be about 280 °C. The sensor shows excellent selectivity to ethanol. For various ethanol concentrations (1 ppm–20 ppm), the response and recovery times are around 3 s and 15 s at the working temperature of 280 °C, respectively. Specifically, the <jats:italic>α</jats:italic>-Fe<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> sensor exhibits a response shift less than 6% to ethanol at 280 °C when the relative humidity (RH) increases from 30% to 70%. The good tolerance to humidity variation makes the sensor suitable for reliable applications in Internet of Things (IoT) in realistic environments. In addition, the sensor shows great long-term repeatability and stability towards ethanol. A possible gas sensing mechanism is proposed.</jats:p>

<jats:p>We present a new charge trapping memory (CTM) device with the Au/Ga<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>/SiO<jats:sub>2</jats:sub>/Si structure, which is fabricated by using the magnetron sputtering, high-temperature annealing, and vacuum evaporation techniques. Transmission electron microscopy diagrams show that the thickness of the SiO<jats:sub>2</jats:sub> tunneling layer can be controlled by the annealing temperature. When the devices are annealed at 760 °C, the measured <jats:italic>C</jats:italic>–<jats:italic>V</jats:italic> hysteresis curves exhibit a maximum 6 V memory window under a ±13 V sweeping voltage. In addition, a slight degradation of the device voltage and capacitance indicates the robust retention properties of flat-band voltage and high/low state capacitance. These distinctive advantages are attributed to oxygen vacancies and inter-diffusion layers, which play a critical role in the charge trapping process.</jats:p>

<jats:p>Lateral two-dimensional (2D) heterostructures have opened up unprecedented opportunities in modern electronic device and material science. In this work, electronic properties of size-dependent MoTe<jats:sub>2</jats:sub>/WTe<jats:sub>2</jats:sub> lateral heterostructures (LHSs) are investigated through the first-principles density functional calculations. The constructed periodic multi-interfaces patterns can also be defined as superlattice structures. Consequently, the direct band gap character remains in all considered LHSs without any external modulation, while the gap size changes within little difference range with the building blocks increasing due to the perfect lattice matching. The location of the conduction band minimum (CBM) and the valence band maximum (VBM) will change from <jats:italic>P</jats:italic>-point to <jats:italic>Γ</jats:italic>-point when <jats:italic>m</jats:italic> plus <jats:italic>n</jats:italic> is a multiple of 3 for <jats:italic>A</jats:italic>-<jats:italic>mn</jats:italic> LHSs as a result of Brillouin zone folding. The bandgap located at high symmetry <jats:italic>Γ</jats:italic>-point is favourable to electron transition, which might be useful to optoelectronic device and could be achieved by band engineering. Type-II band alignment occurs in the MoTe<jats:sub>2</jats:sub>/WTe<jats:sub>2</jats:sub> LHSs, for electrons and holes are separated on the opposite domains, which would reduce the recombination rate of the charge carriers and facilitate the quantum efficiency. Moreover, external biaxial strain leads to efficient bandgap engineering. MoTe<jats:sub>2</jats:sub>/WTe<jats:sub>2</jats:sub> LHSs could serve as potential candidate materials for next-generation electronic devices.</jats:p>

<jats:p>Slave-particle method is a powerful tool to tackle the correlation effect in quantum many-body physics. Although it has been successfully used to comprehend various intriguing problems, such as Mott metal–insulator transition and Kondo effect, there is still no convincing theory so far on the availability and limitation of this method. The abuse of slave-particle method may lead to wrong physics. As the simplest slave-particle method, <jats:inline-formula> <jats:tex-math><?CDATA ${{\mathbb{Z}}}_{2}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="double-struck">Z</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_10_107103_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> slave spin, which is widely applied to many strongly correlated problems, is highly accessible and researchable. In this work, we will uncover the nature of the <jats:inline-formula> <jats:tex-math><?CDATA ${{\mathbb{Z}}}_{2}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="double-struck">Z</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_10_107103_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> slave-spin method by studying a two-site Hubbard model. After exploring aspects of properties of this toy model, we make a comparative analysis of the results obtained by three methods: (i) slave-spin method on mean-field level, (ii) slave-spin method with gauge constraint, and (iii) the exact solution as a benchmark. We find that, protected by the particle–hole symmetry, the slave-spin mean-field method can recover the static properties of ground state exactly at half filling. Furthermore, in the parameter space where both <jats:italic>U</jats:italic> and <jats:italic>T</jats:italic> are small enough, the slave-spin mean-field method is also reliable in calculating the dynamic and thermal dynamic properties. However, when <jats:italic>U</jats:italic> or <jats:italic>T</jats:italic> is considerably large, the mean-field approximation gives ill-defined behaviors, which result from the unphysical states in the enlarged Hilbert space. These findings lead to our conclusion that the accuracy of slave particle can be guaranteed if we can exclude all unphysical states by enforcing gauge constraints. Our work demonstrates the promising prospect of slave-particle method in studying complex strongly correlated models with specific symmetry or in certain parameter space.</jats:p>

<jats:p>Spintronics is a new discipline focusing on the research and application of electronic spin properties. After the discovery of the giant magnetoresistance effect in 1988, spintronics has had a huge impact on scientific progress and related applications in the development of information technology. In recent decades, the main motivation in spintronics has been efficiently controlling local magnetization using electron flow or voltage rather than controlling the electron flow using magnetization. Using spin–orbit coupling in a material can convert a charge current into a pure spin current (a flow of spin momenta without a charge flow) and generate a spin–orbit torque on the adjacent ferromagnets. The ability of spintronic devices to utilize spin-orbit torques to manipulate the magnetization has resulted in large-scale developments such as magnetic random-access memories and has boosted the spintronic research area. Here in, we review the theoretical and experimental results that have established this subfield of spintronics. We introduce the concept of a pure spin current and spin-orbit torques within the experimental framework, and we review transport-, magnetization-dynamics-, and optical-based measurements and link then to both phenomenological and microscopic theories of the effect. The focus is on the related progress reported from Chinese universities and institutes, and we specifically highlight the contributions made by Chinese researchers.</jats:p>

<jats:p>The optical response of an inverted InAs/GaSb quantum well is studied theoretically. The influence of an in-plane magnetic field that is applied parallel to the quantum well is considered. This in-plane magnetic field will induce a dynamical polarization even when the electric field component of the external optical field is parallel to the quantum well. The electron–electron interaction in the quantum well system will lead to the de-polarization effect. This effect is found to be important and is taken into account in the calculation of the optical response. It is found that the main feature in the frequency dependence of the velocity–velocity correlation function remains when the velocity considered is parallel to the in-plane magnetic field. When the direction of the velocity is perpendicular to the in-plane magnetic field, the de-polarization effect will suppress the oscillatory behavior in the corresponding velocity–velocity correlation function. The in-plane magnetic field can change the band structure of the quantum well drastically from a gapped semiconductor to a no-gapped semi-metal, but it is found that the distribution of the velocity matrix elements or the optical transition matrix elements in the wave vector space has the same two-tadpole topology.</jats:p>

<jats:p>We demonstrate transitions of hopping behaviors for delocalized electrons through the discrete dopant-induced quantum dots in n-doped silicon junctionless nanowire transistors by the temperature-dependent conductance characteristics. There are two obvious transition platforms within the critical temperature regimes for the experimental conductance data, which are extracted from the unified transfer characteristics for different temperatures at the gate voltage positions of the initial transconductance <jats:italic>g</jats:italic> <jats:sub>m</jats:sub> peak in <jats:italic>V</jats:italic> <jats:sub>g1</jats:sub> and valley in <jats:italic>V</jats:italic> <jats:sub>g2</jats:sub>. The crossover temperatures of the electron hopping behaviors are analytically determined by the temperature-dependent conductance at the gate voltages <jats:italic>V</jats:italic> <jats:sub>g1</jats:sub> and <jats:italic>V</jats:italic> <jats:sub>g2</jats:sub>. This finding provides essential evidence for the hopping electron behaviors under the influence of thermal activation and long-range Coulomb interaction.</jats:p>

<jats:p>Recent studies in van der Waals coupled two-dimensional (2D) bilayer materials have demonstrated a new freedom for material engineering by the formation of moiré pattern. By tuning the twist angle between two layers, one can modulate their electronic band structures and therefore the associated electrical transport and optical properties, which are distinct from the original ones of each individual layer. These new properties excite great passion in the exploration of new quantum states and possible applications of 2D bilayers. In this article, we will mainly review the prevailing fabrication methods and emerging physical properties of twisted bilayer materials and lastly give out a perspective of this topic.</jats:p>

<jats:p>We study the spin-dependent thermopower in a double-quantum-dot (DQD) embedded between the left and right two-dimensional electron gases (2DEGs) in doped quantum wells under an in-plane magnetic field. When the separation between the DQD is smaller than the Fermi wavelength in the 2DEGs, the asymmetry in the dots’ energy levels leads to pronounced quantum interference effects characterized by the Dicke line-shape of the conductance, which are sensitive to the properties of the 2DEGs. The magnitude of the thermopower, which denotes the generated voltage in response to an infinitesimal temperature difference between the two 2DEGs under vanishing charge current, will be obviously enhanced by the Dicke effect. The application of the in-plane magnetic field results in the polarization of the spin-up and spin-down conductances and thermopowers, and enables an efficient spin-filter device in addition to a tunable pure spin thermopower in the absence of its charge counterpart.</jats:p>

<jats:p>SmB<jats:sub>6</jats:sub>, a topological Kondo insulator, with a gapped bulk state and metallic surface state has aroused great research interest. Here, we report an exotic hysteresis behavior of magnetoresistance in individual SmB<jats:sub>6</jats:sub> nanowire in a temperature range in which both surface and bulk states contribute to the total conductance. Under a magnetic field parallel to the SmB<jats:sub>6</jats:sub> nanowire, the resistance suddenly increases at the turning point from up-sweep to down-sweep of the magnetic field. The magnetoresistance hysteresis loops are well consistent with the magnetocaloric effect. Our results suggest that the SmB<jats:sub>6</jats:sub> nanowires possess potential applications in the magnetic cooling technology.</jats:p>