The discovery of high temperature superconductivity in FeSe films on SrTiO₃ substrate has inspired great experimental and theoretical interests. First-principles density functional theory calculations, which have played an important role in the study of bulk iron-based superconductors, also participate in the investigation of interfacial superconductivity. In this article, we review the calculation results on the electronic and magnetic structures of FeSe epitaxial films, emphasizing on the interplay between different degrees of freedom, such as charge, spin, and lattice vibrations. Furthermore, the comparison between FeSe monolayer and bilayer films on SrTiO₃ is discussed.

This paper reviews some of the recent progresses in the study of high temperature superconductivity in the interface between a single unit cell FeSe and SrTiO₃. It offers the author’s personal view of why T_c is high and how to further increase it.

The stability of the first-order and second-order solution moments for a Harrison-type predator-prey model with parametric Gaussian white noise is analyzed in this paper. The moment equations of the system solution are obtained under Itô interpretations. The delay-independent stable condition of the first-order moment is identical to that of the deterministic delayed system, and the delay-independent stable condition of the second-order moment depends on the noise intensities. The corresponding critical time delays are determined once the stabilities of moments lose. Further, when the time delays are greater than the critical time delays, the system solution becomes unstable with the increase of noise intensities. Finally, some numerical simulations are given to verify the theoretical results.

This paper focuses on analyzing the composite dynamic behaviors of two meminductors in serial and parallel connections with different polarities. Based on the constitutive relations, two time-integral-of-flux (TIF) controlled meminductors are adopted to theoretically demonstrate the variation of memductance in terms of TIF, charge, flux, and current. By utilizing a floating memristor-less meminductor emulator, the theoretical analysis reported in this paper is confirmed via a PSPICE simulation study and hardware experiment. Good agreement among theoretical analysis, simulation, and hardware validation confirms that dual meminductor circuits in composite connections behave as a new meminductor with higher complexity.

The field ionization process of the Eu 4f⁷6snp Rydberg states, converging to the first ionization limit, 4f⁷6s ⁹S₄, is systematically investigated. The spectra of the Eu 4f⁷6snp Rydberg states are populated with three-step laser excitation, and detected by electric field ionization (EFI) method. Two different kinds of the EFI pulses are applied after laser excitation to observe the possible impacts on the EFI process. The exact EFI ionization thresholds for the 4f⁷6snp Rydberg states can be determined by observing the corresponding EFI spectra. In particular, some structures above the EFI threshold are found in the EFI spectra, which may be interpreted as the effect from black body radiation (BBR). Finally, the scaling law of the EFI threshold for the Eu 4f⁷6snp Rydberg states with the effective quantum number is built.

For most of the conventional crystals with low-index surfaces, the hopping between the nearest neighbor (1NN) crystal planes (CPs) is dominant and the ones from the nNN (2≤q < ∞) CPs are relatively weak, considered as small perturbations. The recent theoretical analysis^[1] has demonstrated the absence of surface states at the level of the hopping approximation between the 1NN CPs when the original infinite crystal has the geometric reflection symmetry (GRS) for each CP. Meanwhile, based on the perturbation theory, it has also been shown that small perturbations from the hopping between the nNN (2≤n<∞) CPs and surface relaxation have no impact on the above conclusion. However, for the crystals with strong intrinsic spin-orbit coupling (SOC), the dominant terms of intrinsic SOC associate with two 1NN bond hoppings. Thus SOC will significantly contribute the hoppings from the 1NN and/or 2NN CPs except the ones within each CP. Here, we will study the effect of the hopping between the 2NN CPs on the surface states in model crystals with three different type structures (Type I: “…-P-P-P-P-…”, Type II: “…-P-Q-P-Q-” and Type III: “…-P=Q-P=Q-…” where P and Q indicate CPs and the signs “-” and “=” mark the distance between the 1NN CPs). In terms of analytical and numerical calculations, we study the behavior of surface states in three types after the symmetric/asymmetric hopping from the 2NN CPs is added. We analytically prove that the symmetric hopping from the 2NN CPs cannot induce surface states in Type I when each CP has only one electron mode. The numerical calculations also provide strong support for the conclusion, even up to 5NN. However, in general, the coupling from the 2NN CPs (symmetric and asymmetric) is favorable to generate surface states except Type I with single electron mode only.

In this paper, Al₂O₃ ultrathin film used as the surface passivation layer for AlGaN/GaN high electron mobility transistor (HEMT) is deposited by thermal atomic layer deposition (ALD), thereby avoiding plasma-induced damage and erosion to the surface. A comparison is made between the surface passivation in this paper and the conventional plasma enhanced chemical vapor deposition (PECVD) SiN passivation. A remarkable reduction of the gate leakage current and a significant increase in small signal radio frequency (RF) performance are achieved after applying Al₂O₃+BCB passivation. For the Al₂O₃+BCB passivated device with a 0.7 μ gate, the value of f_max reaches up to 100 GHz, but it decreases to 40 GHz for SiN HEMT. The f_max/f_t ratio (≥ 4) is also improved after Al₂O₃+BCB passivation. The capacitance-voltage (C-V) measurement demonstrates that Al₂O₃+BCB HEMT shows quite less density of trap states (on the order of magnitude of 10¹⁰ cm^-2) than that obtained at commonly studied SiN HEMT.

Electrochemical method has been used to insert K/Na into FeSe lattice to prepare alkali-intercalated iron selenides at room temperature. Magnetization measurement reveals that K_xFe₂Se₂ and Na_xFe₂Se₂ are superconductive at 31 K and 46 K, respectively. This is the first successful report of obtaining metal-intercalated FeSe-based high-temperature superconductors using electrochemical method. It provides an effective route to synthesize metal-intercalated layered compounds for new superconductor exploration.

The intrinsic dynamics of two interacting electric polarized nanorods is theoretically investigated. The relative motion between them caused by electric dipole-dipole interaction is derived based on the generalized Lagrangian formulation. The results show that the relative translation and rotation are nonlinear and closely dependent on the initial configuration of the two nanorods. Furthermore, the general conditions of the initial configuration, which determine the two nanorods to repel or attract each other at the initial time, are obtained. The two-dimensional relative motion of the two nanorods shows that the antiparallel and head-to-tail ordering stable self-assembly are respectively formed in two planar initial configurations. For different three-dimensional initial configurations, the interesting dynamic relative attraction, repulsion, and oscillation with rotation are respectively realized. Finally, the theoretical schemes which realize the relaxing, direct head-to-tail ordering, and direct antiparallel ordering stable self-assembly are presented according to the different modes of the motion of the nanoparticles. Some of our results agree well with the results of experiments and simulations.

In this work, pure α-Fe₂O₃ and Er₂O₃-Fe₂O₃ nanotubes were synthesized by a simple single-capillary electrospinning technology followed by calcination treatment. The morphologies and crystal structures of the as-prepared samples were characterized by scanning electron microscopy and x-ray diffraction, respectively. The gas-sensing properties of the as-prepared samples have been researched, and the result shows that the Er₂O₃-Fe₂O₃ nanotubes exhibit much better sensitivity to ethanol. The response value of Er₂O₃-Fe₂O₃ nanotubes to 10 ppm ethanol is 21 at the operating temperature 240°, which is 14 times larger than that of pure α-Fe₂O₃ nanotubes (response value is 1.5). The ethanol sensing properties of α-Fe₂O₃ nanotubes are remarkably enhanced by doping Er, and the lowest detection limit of Er₂O₃-Fe₂O₃ nanotubes is 300 ppb, to which the response value is about 2. The response and recovery times are about 4 s and 70 s to 10 ppm ethanol, respectively. In addition, the Er₂O₃-Fe₂O₃ nanotubes possess good selectivity and long-term stability.

Our current understanding about the AS level topology of the Internet is based on measurements and inductive-type models which set up rules describing the behavior (node and edge dynamics) of the individual ASes and generalize the consequences of these individual actions for the complete AS ecosystem using induction. In this paper we suggest a third, deductive approach in which we have premises for the whole AS system and the consequences of these premises are determined through deductive reasoning. We show that such a deductive approach can give complementary insights into the topological properties of the AS graph. While inductive models can mostly reflect high level statistics (e.g., degree distribution, clustering, diameter), deductive reasoning can identify omnipresent subgraphs and peering likelihood. We also propose a model, called YEAS, incorporating our deductive analytical findings that produces topologies contain both traditional and novel metrics for the AS level Internet.