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<jats:p>Iron-based superconductor family Fe<jats:italic>X</jats:italic> (<jats:italic>X</jats:italic> = S, Se, Te) has been one of the research foci in physics and material science due to their record-breaking superconducting temperature (FeSe film) and rich physical phenomena. Recently, FeS, the least studied Fe<jats:italic>X</jats:italic> compound (due to the difficulty in synthesizing high quality macroscopic crystals) attracted much attention because of its puzzling superconducting pairing symmetry. In this work, combining scanning tunneling microscopy and angle resolved photoemission spectroscopy (ARPES) with sub-micron spatial resolution, we investigate the intrinsic electronic structures of superconducting FeS from individual single crystalline domains. Unlike FeTe or FeSe, FeS remains identical tetragonal structure from room temperature down to 5 K, and the band structures observed can be well reproduced by our <jats:italic>ab-initio</jats:italic> calculations. Remarkably, mixed with the 1 × 1 tetragonal metallic phase, we also observe the coexistence of <jats:inline-formula> <jats:tex-math><?CDATA $\sqrt{5}\times \sqrt{5}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msqrt> <mml:mn>5</mml:mn> </mml:msqrt> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mn>5</mml:mn> </mml:msqrt> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_4_047401_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> reconstructed insulating phase in the crystal, which not only helps explain the unusual properties of FeS, but also demonstrates the importance of using spatially resolved experimental tools in the study of this compound.</jats:p>

<jats:p>The cubic pyrochlore Dy<jats:sub>2</jats:sub>Pt<jats:sub>2</jats:sub>O<jats:sub>7</jats:sub> was synthesized under 4 GPa and 1000 °C and its magnetic and thermodynamic properties were characterized by DC and AC magnetic susceptibility and specific heat down to 0.1 K. We found that Dy<jats:sub>2</jats:sub>Pt<jats:sub>2</jats:sub>O<jats:sub>7</jats:sub> does not form long-range magnetic order, but displays characteristics of canonical spin ice such as Dy<jats:sub>2</jats:sub>Ti<jats:sub>2</jats:sub>O<jats:sub>7</jats:sub>, including (1) a large effective moment 9.64 <jats:italic>μ</jats:italic> <jats:sub>B</jats:sub> close to the theoretical value and a small positive Curie–Weiss temperature <jats:italic>θ</jats:italic> <jats:sub>CW</jats:sub> = +0.77 K signaling a dominant ferromagnetic interaction among the Ising spins; (2) a saturation moment ∼4.5 <jats:italic>μ</jats:italic> <jats:sub>B</jats:sub> being half of the total moment due to the local 〈111〉 Ising anisotropy; (3) thermally activated spin relaxation behaviors in the low (∼1 K) and high (∼20 K) temperature regions with different energy barriers and characteristic relaxation time; and most importantly, (4) the presence of a residual entropy close to Pauling’ estimation for water ice.</jats:p>

<jats:p>We revisit the reversible magnetocaloric effect of itinerant ferromagnet Mn<jats:sub>3</jats:sub>GaC near the ferromagnetic to paramagnetic phase transition by adopting the experimental and theoretical methods and critical behavior of Mn-rich Mn<jats:sub>3</jats:sub>GaC with an enhanced FM interaction. Landau theory model cannot account for temperature dependent magnetic entropy change which is estimated from thermal magnetic methods only considering magnetoelastic coupling and the electron–electron interaction, apart from molecular mean-field model. Critical behavior is studied by adopting the modified Arrott plot, Kouvel–Fisher plot, and critical isotherm analysis. With these critical exponents, experimental data below and above <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> collapse into two universal branches, fulfilling the single scaling equation <jats:italic>m</jats:italic> = <jats:italic>f</jats:italic> <jats:sub>±</jats:sub>(<jats:italic>h</jats:italic>), where <jats:italic>m</jats:italic> and <jats:italic>h</jats:italic> are renormalized magnetization and field. Critical exponents are confirmed by Widom scaling law and just between mean-field model and three-dimensional Heisenberg model, as the evidence for the existence of long-range ferromagnetic interaction. With increasing the Mn content, <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> increases monotonously and critical exponents increases accordingly. The exchange distance changes from <jats:italic>J</jats:italic>(<jats:italic>r</jats:italic>) ∼ <jats:italic>r</jats:italic> <jats:sup>–4.68</jats:sup> for <jats:italic>x</jats:italic> = 0 to <jats:italic>J</jats:italic>(<jats:italic>r</jats:italic>) ∼ <jats:italic>r</jats:italic> <jats:sup>–4.71</jats:sup> for <jats:italic>x</jats:italic> = 0.08, respectively, which suggests the competition of the Mn–Mn direct interaction and the itinerant Mn–C–Mn hybridization. The possible mechanism is proposed.</jats:p>

<jats:p>The multicaloric effect refers to the thermal response of a solid material driven by simultaneous or sequential application of more than one type of external field. For practical applications, the multicaloric effect is a potentially interesting strategy to improve the efficiency of refrigeration devices. Here, the state of the art in multi-field driven multicaloric effect is reviewed. The phenomenology and fundamental thermodynamics of the multicaloric effect are well established. A number of theoretical and experimental research approaches are covered. At present, the theoretical understanding of the multicaloric effect is thorough. However, due to the limitation of the current experimental technology, the experimental approach is still in progress. All these researches indicated that the thermal response and effective reversibility of multiferroic materials can be improved through multicaloric cycles to overcome the inherent limitations of the physical mechanisms behind single-field-induced caloric effects. Finally, the viewpoint of further developments is presented.</jats:p>

<jats:p>Designed Zr<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Si<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>O<jats:sub>2</jats:sub> films with combining bent and flat energy bands are employed as a charge trapping layer for memory capacitors. Compared to a single bent energy band, the bandgap structure with combining bent and flat energy bands exhibits larger memory window, faster program/erase speed, lower charge loss even at 200 °C for 10<jats:sup>4</jats:sup> s, and wider temperature insensitive regions. The tunneling thickness together with electron recaptured efficiency in the trapping layer, and the balance of two competing electron loss mechanisms in the bent and flat energy band regions collectively contribute to the improved memory characteristics. Therefore, the proposed Zr<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Si<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>O<jats:sub>2</jats:sub> with combining bent and flat energy bands should be a promising candidate for future nonvolatile memory applications, taking into consideration of the trade-off between the operation speed and retention characteristics.</jats:p>

<jats:p>Ionic liquids have received wide attention due to their novel optoelectronic structures and devices as an optical means of regulating electricity. However, the quantitative testing and analysis of refractive index of ionic liquids under electric field are rarely carried out. In the present study, an experimental apparatus including a hollow prism is designed to measure the refractive indices of ionic liquids under different electric fields. Five groups of imidazole ionic liquids are experimentally investigated and an inversion is performed to determine the refractive indices under electric fields. The error propagation analysis of the apex angle and the minimum deflection angle are conducted, and the machining accuracy requirements of the hollow prism are determined. The results show that the refractive indices of imidazole ionic liquids change with the light wavelength, following a downward convex parabola. Furthermore, the refractive index decreases with the carbon chain length of ionic liquid at a given wavelength, presenting an order of C<jats:sub>3</jats:sub>MImI &gt; C<jats:sub>4</jats:sub>MImI &gt; C<jats:sub>5</jats:sub>MImI &gt; C<jats:sub>3</jats:sub>MImBr &gt; C<jats:sub>3</jats:sub>MImBF<jats:sub>4</jats:sub>. Notably, the refractive index of imidazole ionic liquid exhibits a nonlinear change with the applied voltage at 546 nm and a monotonical decrease at 1529 nm. Besides, the variation of refractive index at 1529 nm with the applied voltage is larger than that at 546 nm and 1013 nm. Importantly, the variation of refractive index is contrary to that of absorption coefficient under electric field. This study illustrates that the theory of electrode and carrier transport can be used to explain the law of variation of <jats:italic>n</jats:italic>–<jats:italic>k</jats:italic> value of ionic liquid under the electric field, and provides the support for the evaluation of physical properties of ionic liquids, the measurement of optical functional parameters and the regulation of electric–optic performances of optical devices.</jats:p>

<jats:p>It is observed that the radiative recombination rate in InGaN-based light-emitting diode decreases with lattice temperature increasing. The effect of lattice temperature on the radiative recombination rate tends to be stable at high injection. Thus, there should be an upper limit for the radiative recombination rate in the quantum well with the carrier concentration increasing, even under the same lattice temperature. A modified and easily used ABC-model is proposed. It describes that the slope of the radiative recombination rate gradually decreases to zero, and further reaches a negative value in a small range of lattice temperature increasing. These provide a new insight into understanding the dependence of the radiative recombination rate on lattice temperature and carrier concentration in InGaN-based light-emitting diode.</jats:p>

<jats:p>Laser powder bed fusion (LPBF), like many other additive manufacturing techniques, offers flexibility in design expected to become a disruption to the manufacturing industry. The current cost of LPBF process does not favor a try-and-error way of research, which makes modelling and simulation a field of superior importance in that area of engineering. In this work, various methods used to overcome challenges in modeling at different levels of approximation of LPBF process are reviewed. Recent efforts made towards a reliable and computationally effective model to simulate LPBF process using finite element (FE) codes are presented. A combination of ray-tracing technique, the solution of the radiation transfer equation and absorption measurements has been used to establish an analytical equation, which gives a more accurate approximation of laser energy deposition in powder-substrate configuration. When this new analytical energy deposition model is used in in FE simulation, with other physics carefully set, it enables us to get reliable cooling curves and melt track morphology that agree well with experimental observations. The use of more computationally effective approximation, without explicit topological changes, allows to simulate wider geometries and longer scanning time leading to many applications in real engineering world. Different applications are herein presented including: prediction of printing quality through the simulated overlapping of consecutive melt tracks, simulation of LPBF of a mixture of materials and estimation of martensite inclusion in printed steel.</jats:p>

<jats:p>The dynamics of granular material discharging from a cuboid but thin hopper, including the hopper flow and granular jet, are investigated via discrete element method (DEM) simulations. The slot width is varied to study its influence on the flow. It is found the flow in the cuboid hopper has similarity with the flow in two-dimensional (2D) hopper. When the slot width is large, the flowrate is higher than the predicted value from Beverloo’s law and the velocity distribution is not Gaussian-like. For granular jet, there is a transition with varying slot width. For large slot width, there is a dense core in the jet and the variations of velocities and density are relatively small. Finally, the availability of continuum model is assessed and the results show that the performance with large slot width is better than that with small slot width.</jats:p>

<jats:p>We have successfully prepared GaN based high electron mobility transistors (HEMTs) on metallic substrates transferred from silicon substrates by electroplating technique. GaN HEMTs on Cu substrates are demonstrated to basically have the same good electric characteristics as the chips on Si substrates. Furthermore, the better heat dissipation of HEMTs on Cu substrates compared to HEMTs on Si substrates is clearly observed by thermoreflectance imaging, showing the promising potential for very high-power and high-temperature operation. This work shows the outstanding ability of HEMT chips on Cu substrates for solving the self-heating effect with the advantages of process simplicity, high yield, and low production requirement.</jats:p>