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The interplay between topology and valley degree of freedom has attracted much interest because it can realize new phenomena and applications. Here, based on first-principles calculations, we demonstrate intrinsically valley-polarized quantum anomalous Hall effect in monolayer ferrovalley material: Janus VSiGeN4, of which the edge states are chiral-spin-valley locking. Besides, a small tensile or compressive strain can drive phase transition in the material from valley-polarized quantum anomalous Hall state to half-valley-metal state. With the increase of the strain, the material turns into ferrovalley semiconductor with valley anomalous Hall effect. The origin of phase transition is sequent band inversion of V d orbital at K valley. Moreover, we find that phase transition causes the sign reversal of Berry curvature and induces different polarized light absorption in different valley states. Our work provides an ideal material platform for practical applications and experimental exploration of the interplay between topology, spintronics, and valleytronics., Comment: 8 pages, 6 figures

Two-dimensional (2D) ferromagnetic materials with high Curie temperatures (TC) and tunable physical properties are crucial to the development of nanoscale spintronics devices. Here, we investigate the newly synthesized iodinene using first-principles calculations. Our results show that doping carriers in monolayer and bilayer iodinene can easily introduce itinerant ferromagnetism due to a flatband structure near the Fermi level, and that the associated TC is higher than room temperature. Moreover, we find that a structural phase transition can be achieved through the application of moderate tensile strain for both monolayer and bilayer iodinene. The magnetic moment, Curie temperature, band structure, carrier effective mass, and optical absorption can be changed significantly through this phase transition, and the transition can also lead to a magnetic phase transition with an appropriate doping concentration. Our work provides a feasible approach for designing 2D magnetic materials with potential for application in microelectronics devices.

The nanoscale characteristics of semiconducting transition metal dichalcogenides (TMDCs) are largely determined by their photonic, mechanical, magnetic, thermal, and electronic properties, which can be modulated by adjusting thickness and radiation treatments. In this paper, gamma-rays were applied to irradiate the materials with one to six layers, based on which a comparison was drawn of the frictional and electrical properties before and after irradiation. The changes on a few-layer WSe2 were investigated using Raman spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, transmission electron microscopy, force friction microscopy, and Kelvin probe force microscopy. Under the context of irradiation, there was a phenomenon found different than previously reported. The friction force of WSe2 nano-flakes increased from monolayer to bilayer, decreased at tri-layer, and then increased on a continued basis with thickness. It is suggested that the gamma-ray irradiation treatment could be effective in improving frictional and electronic properties. The range of change to the surface contact potential difference (CPD) was narrowed, and the stability of the device surface potential was enhanced. The continuum mechanics theory was applied to explore the friction force variation between different thickness layers. Based on the puckering effect of tip-flake adhesion, the friction force was determined by bending stiffness. The thermal treatment of WSe2 nanoflakes had a significant impact on the CPD between the sample and the test tip. After thermal treatment, the surface potential increased from one to five layers with thickness. These phenomena were explained in detail. The research contributes to enriching nanotribology and electrical theory in addition to promoting the use of semiconducting TMDCs for nano-components’ design.

By introducing a suitable barrier, carrier filtering can yield a high Seebeck coefficient by filtering out electrons (or holes) with low energy. To understand carrier filtering in a PbTe/SrTe interface, the first-principles method and semiclassical Boltzmann theory are used to investigate electronic structures and Seebeck coefficients of PbTe/SrTe (110) and (100) interfaces. The PbTe/SrTe heterostructure is found to be a type-I interface that can form an energy barrier that filters low-energy carriers. Such carrier filtering induces a large in-plane Seebeck coefficient of ∼277 μV K−1 (T = 600 K) with a fixed carrier concentration of 1.6 × 1020 cm−3. This large in-plane Seebeck coefficient is attributed to the Te-p states and the strong asymmetry of the transmission. Additionally, the values of the Seebeck coefficient of p-type PbTe/SrTe (110) are larger than those of the n-type one, and the electronic properties of the PbTe/SrTe (100) interface are similar to those of the PbTe/SrTe (110) interface.

We theoretically investigate the optical properties of two-intersecting nanorings (TINR), which exhibit a pronounced Fano resonance in the near-infrared region. A multiple-layer plasmon hybridization model is proposed to explain the reasons and forming processes of the Fano resonance. The dependence of the Fano resonance on the intersecting distance is also demonstrated. Moreover, the presented two-intersecting nanorings are employed as a biosensor exhibiting a 3-fold improvement of the figure of merit than that of a single-ring biosensor with the same resonant wavelength.

Density functional theory calculations by using both generalized gradient approximation (GGA) method and the GGA with considering strong correlation effect (GGA+U) were performed to elucidate the effect of Ce-4f orbit on the electronic structure of ZnO. It is found that after the cerium incorporation, a new localized band appears between the valence and conduction bands, which corresponds to the majority spin of Ce-4f states. It is this localized band that constructs a bridge between the valence and conduction states, which will improve the optical performance of ZnO. ZnO:Ce is a degenerate semiconductor. The strong correlation effect is very important for the 4f orbit of the Ce atom in ZnO:Ce. The mismatch of the majority and minority spin for the Ce-4f, Ce-5d states and the spin-polarized holes in O-2p states induced by Ce doping leads to the presence of the magnetic order for ZnO:Ce. We also studied the band structure and optical properties of ZnO:Ce with lacking one electron and two electrons, respect...