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<jats:p>Motivated by recent experimental progress on triangular lattice heavy-fermion compounds, we investigate possible Lifshitz transitions and the scanning tunnel microscope (STM) spectra of the Kondo–Heisenberg model on the triangular lattice. In the heavy Fermi liquid state, the introduced Heisenberg antiferromagnetic interaction (<jats:italic>J</jats:italic> <jats:sub>H</jats:sub>) results in the twice Lifshitz transition at the case of the nearest-neighbour electron hopping but with next-nearest-neighbour hole hopping and the case of the nearest-neighbour hole hopping but with next-nearest-neighbour electron hopping, respectively. Driven by <jats:italic>J</jats:italic> <jats:sub>H</jats:sub>, the Lifshitz transitions on triangular lattice are all continuous in contrast to the case on square lattice. Furthermore, the STM spectra shows rich line-shape which is influenced by the Kondo coupling <jats:italic>J</jats:italic> <jats:sub>K</jats:sub>, the Heisenberg antiferromagnetic interaction <jats:italic>J</jats:italic> <jats:sub>H</jats:sub>, and the ratio of the tunneling amplitude of f-electron <jats:italic>t</jats:italic> <jats:sub>f</jats:sub> versus conduction electron <jats:italic>t</jats:italic> <jats:sub>c</jats:sub>. Our work provides a possible scenario to understand the Fermi surface topology and the quantum critical point in heavy-fermion compounds.</jats:p>

<jats:p>We have carried out point-contact spectroscopy (PCS) measurements on one family of antiferromagnetic Kondo semiconductor Ce<jats:italic>T</jats:italic> <jats:sub>2</jats:sub>Al<jats:sub>10</jats:sub> (<jats:italic>T</jats:italic> = Ru and Os) with a Nèel temperature <jats:italic>T</jats:italic> <jats:sub>N</jats:sub> ∼ 27.5 and 28.5 K, respectively. Their PCS conductance curves both exhibit a characteristic coherent double-peak-structure at temperatures below <jats:italic>T</jats:italic> <jats:sub>N</jats:sub>, signaling an AFM gap around the Fermi surface. The temperature dependent AFM gap <jats:italic>Δ</jats:italic> <jats:sub>1</jats:sub> follows a Bardeen–Cooper–Schrieffer (BCS)-like mean-field behavior with a moderate gap anisotropy for PCS along different crystal axes. Another asymmetric gap-like feature is observed for both compounds at temperatures far below <jats:italic>T</jats:italic> <jats:sub>N</jats:sub>, which is consistent with opening of a new hybridization gap <jats:italic>Δ</jats:italic> <jats:sub>h</jats:sub> inside the long-range ordered AFM state. Our results suggest a common itinerant nature of the anomalous AFM ordering, constraining theoretical models to explain the AFM origin in CeRu<jats:sub>2</jats:sub>Al<jats:sub>10</jats:sub> and CeOs<jats:sub>2</jats:sub>Al<jats:sub>10</jats:sub>.</jats:p>

<jats:p>We report the epitaxial growth of monolayer copper arsenide (CuAs) with a honeycomb lattice on Cu(111) by molecular beam epitaxy (MBE). Scanning tunneling microscopy (STM), low energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) verify the <jats:inline-formula> <jats:tex-math><?CDATA $\sqrt{3}\times \sqrt{3}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msqrt> <mml:mn>3</mml:mn> </mml:msqrt> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mn>3</mml:mn> </mml:msqrt> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_7_077301_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> superlattice of monolayer CuAs on Cu(111) substrate. Angle-resolved photoemission spectroscopy (ARPES) measurements together with DFT calculations demonstrate the electronic band structures of monolayer CuAs and reveal its metallic nature. Further calculations show that charge transfer from Cu(111) substrate to monolayer CuAs lifts the Fermi level and tunes the band structure of the monolayer CuAs. This high-quality epitaxial monolayer CuAs with potential tunable band gap holds promise on the applications in nano-electronic devices.</jats:p>

<jats:p>The valley splitting has been realized in the graphene/Ni heterostructure with the splitting value of 14 meV, and the obtained valley injecting efficiency from the heterostructure into graphene was 6.18% [<jats:italic>Phys. Rev. B</jats:italic> <jats:bold>92</jats:bold> 115404 (2015)]. In this paper, we report a way to improve the valley splitting and the valley injecting efficiency of the graphene/Ni heterostructure. By intercalating an Au monolayer between the graphene and the Ni, the split can be increased up to 50 meV. However, the valley injecting efficiency is not improved because the splitted valley area of graphene moves away from the Fermi level. Then, we mend the deviation by covering a monolayer of Cu on the graphene. As a result, the valley injecting efficiency of the Cu/graphene/Au/Ni heterostructure reaches 10%, which is more than 60% improvement compared to the simple graphene/Ni heterostructure. Then we theoretically design a valley-injection device based on the Cu/graphene/Au/Ni heterostructure and demonstrate that the valley injection can be easily switched solely by changing the magnetization direction of Ni, which can be used to generate and control the valley-polarized current.</jats:p>

<jats:p>V<jats:sub>5</jats:sub>S<jats:sub>8</jats:sub> is an ideal candidate to explore the magnetism at the two-dimensional (2D) limit. A recent experiment has shown that the V<jats:sub>5</jats:sub>S<jats:sub>8</jats:sub> thin films exhibit an antiferromagnetic (AFM) to ferromagnetic (FM) phase transition with reducing thickness. Here, for the first time, using density functional theory calculations, we report the antiferromagnetic order of bulk V<jats:sub>5</jats:sub>S<jats:sub>8</jats:sub>, which is consistent with the previous experiments. The specific antiferromagnetic order is reproduced when <jats:italic>U</jats:italic> <jats:sub>eff</jats:sub> = 2 eV is applied on the intercalated vanadium atoms within LDA. We find that the origin of the magnetic ordering is from superexchange interaction. We also investigate the thickness-dependent magnetic order in V<jats:sub>5</jats:sub>S<jats:sub>8</jats:sub> thin films. It is found that there is an antiferromagnetic to ferromagnetic phase transition when V<jats:sub>5</jats:sub>S<jats:sub>8</jats:sub> is thinned down to 2.2 nm. The main magnetic moments of the antiferromagnetic and ferromagnetic states of the thin films are located on the interlayered vanadium atoms, which is the same as that in the bulk. Meanwhile, the strain in the thin films also influences the AFM–FM phase transition. Our results not only reveal the magnetic order and origin in bulk V<jats:sub>5</jats:sub>S<jats:sub>8</jats:sub> and thin films, but also provide a set of parameters which can be used in future calculations.</jats:p>

<jats:p>The magnetic and electronic properties of spinel oxide LiV<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub> have been systematically studied by using the spin-polarized first-principles electronic structure calculations. We find that a series of magnetic states, in which the ferromagnetic (FM) V<jats:sub>4</jats:sub> tetrahedra are linked together through the corner-sharing antiferromagnetic (AFM) V<jats:sub>4</jats:sub> tetrahedra, possess degenerate energies lower than those of other spin configurations. The large number of these energetically degenerated states being the magnetic ground state give rise to strong magnetic frustration as well as large magnetic entropy in LiV<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub>. The corresponding band structure and density of states of such a typical magnetic state in this series, i.e., the ditetrahedron (DT) AFM state, demonstrate that LiV<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub> is in the vicinity of a metal–insulator transition. Further analysis suggests that the t<jats:sub>2g</jats:sub> and e<jats:sub>g</jats:sub> orbitals of the V atoms play different roles in the magnetic exchange interactions. Our calculations are consistent with previous experimental measurements and shed light on understanding the exotic magnetism and the heavy-fermion behavior of LiV<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub>.</jats:p>

<jats:p>Bulk iridium ditelluride (IrTe<jats:sub>2</jats:sub>) is a layered material and is known for its interesting electronic and structural properties, such as large spin–orbit coupling, charge ordering, and superconductivity. However, so far there is no experimental study about the fabrication of monolayer IrTe<jats:sub>2</jats:sub>. Here we report the formation of IrTe<jats:sub>2</jats:sub> monolayer on Ir(111) substrate by direct tellurization method. Scanning tunneling microscope (STM) images show the coexistence of 1/5 phase and 1/6 phase structures of IrTe<jats:sub>2</jats:sub> at room temperature. We also obtained STM images showing distorted stripe feature under low temperatures. This stripe feature is possibly induced by the strain between the IrTe<jats:sub>2</jats:sub> monolayer and the metal substrate. Density functional theory (DFT) calculations show that the IrTe<jats:sub>2</jats:sub> monolayer has strong interaction with the underlying Ir(111) substrate.</jats:p>

<jats:p>We simulate the evolution of hydrogen concentration and gas pore formation as equiaxed dendrites grow during solidification of a hypoeutectic aluminum–silicon (Al–Si) alloy. The applied lattice Boltzmann-cellular automaton-finite difference model incorporates the physical mechanisms of solute and hydrogen partitioning on the solid/liquid interface, as well as the transports of solute and hydrogen. After the quantitative validation by the simulation of capillary intrusion, the model is utilized to investigate the growth of the equiaxed dendrites and hydrogen porosity formation for an Al–(5 wt.%)Si alloy under different solidification conditions. The simulation data reveal that the gas pores favorably nucleate in the corners surrounded by the nearby dendrite arms. Then, the gas pores grow in a competitive mode. With the cooling rate increasing, the competition among different growing gas pores is found to be hindered, which accordingly increases the pore number density in the final solidification microstructure. In the late solidification stage, even though the solid fraction is increasing, the mean concentration of hydrogen in the residue melt tends to be constant, corresponding to a dynamic equilibrium state of hydrogen concentration in liquid. As the cooling rate increases or the initial hydrogen concentration decreases, the temperature of gas pore nucleation, the porosity fraction, and the mean porosity size decrease, whilst the mean hydrogen concentration in liquid increases in the late solidification stage. The simulated data present identical trends with the experimental results reported in literature.</jats:p>

<jats:p>SiO<jats:sub>2</jats:sub> nanoparticles were used to regulate the crystallizing process of lead halide perovskite films prepared by the sequential deposition method, which was used in the low-temperature-processed, carbon-electrode-basing, hole-conductor-free planar perovskite solar cells. It was observed that, after adding small amount of SiO<jats:sub>2</jats:sub> precursor (1 vol%) into the lead iodide solution, performance parameters of open-circuit voltage, short-circuit current and fill factor were all upgraded, which helped to increase the power conversion efficiency (reverse scan) from 11.44(± 1.83)% (optimized at 12.42%) to 14.01(±2.14)% (optimized at 15.28%, AM 1.5G, 100 mW/cm<jats:sup>2</jats:sup>). Transient photocurrent decay curve measurements showed that, after the incorporation of SiO<jats:sub>2</jats:sub> nanoparticles, charge extraction was accelerated, while transient photovoltage decay and dark current curve tests both showed that recombination was retarded. The improvement is due to the improved crystallinity of the perovskite film. X-ray diffraction and scanning electron microscopy studies observed that, with incorporation of amorphous SiO<jats:sub>2</jats:sub> nanoparticles, smaller crystallites were obtained in lead iodide films, while larger crystallites were achieved in the final perovskite film. This study implies that amorphous SiO<jats:sub>2</jats:sub> nanoparticles could regulate the coarsening process of the perovskite film, which provides an effective method in obtaining high quality perovskite film.</jats:p>