Feng Yuan

In this work, gallium arsenide (GaAs), which has an adjustable band gap and low cost, was adopted as an absorption layer in which KNbO₃, having good dielectric, photoelectric, and piezoelectric properties, served as a scattering element for the improvement in absorption efficiency of solar cells. Benefited by the high absorption efficiency of KNbO₃, the utilization of the ultraviolet and infrared bands for solar cells can be strengthened. In addition, the ferroelectric and photovoltaic characteristics of KNbO₃ enable the realization of decreased thickness of solar cells. Based on the simulation of the shape, width, and period of the scattering element, the effect of the thickness of the scattering element on the absorption efficiency, quantum efficiency, and total efficiency of absorption efficiency was comprehensively simulated. The results show that the absorption layer delivers the optimal performance when using a hexagonal KNbO₃ scattering element. The absorption efficiency of the GaAs absorption layer with KNbO₃ as the scattering element is increased by 28.42% compared with that of a GaAs absorption layer with empty holes. In addition, the quantum efficiency is maintained above 98% and the total efficiency is 91.59%. At the same time, the efficiency of such an absorption layer is still above 90% when the angle ranges from 0 to 70°. This work provides theoretical guidance for the rational design of solar cells based on photonic crystal structures.

Based on the two-dimensional (2D) attractive Fermi-Hubbard model with Rashba spin–orbit coupling (SOC), the SOC strength and Zeeman field dependences of the phase diagram are investigated by calculating the pairing gap self-consistently. The results reveal that the phase transition from the BCS superfluid to the topological superfluid happens under proper Zeeman field strength and SOC strength. In particular, in contrast to the BCS superfluid decreasing monotonically as the SOC strength increasing, the topological superfluid region shows a dome with the SOC strength increasing. An optimal region in the phase diagram to find the topological superfluid can be found, which is important to realize the topological superfluid in optical lattice experimentally. Then we obtain the change of both band structure and density of states (DOSs) during the topological phase transition, and explain the four peaks of DOS in the topological superfluid by the topology change of the low-energy branch of quasiparticle energy spectra. Moreover, the topological superfluid can be suppressed by the doping concentration.

We performed high-pressure transport studies on the flat-band Kagome compounds, Pd₃P₂(S_{1 – x} Se _x )₈ (x = 0, 0.25), with a diamond anvil cell. For both compounds, the resistivity exhibits an insulating behavior with pressure up to 17 GPa. With pressure above 20 GPa, a metallic behavior is observed at high temperatures in Pd₃P₂S₈, and superconductivity emerges at low temperatures. The onset temperature of superconducting transition T _C rises monotonically from 2 K to 4.8 K and does not saturate with pressure up to 43 GPa. For the Se-doped compound Pd₃P₂(S_0.75Se_0.25)₈, the T _C is about 1.5 K higher than that of the undoped one over the whole pressure range, and reaches 6.4 K at 43 GPa. The upper critical field with field applied along the c axis at typical pressures is about 50% of the Pauli limit, suggesting a 3D superconductivity. The Hall coefficient in the metallic phase is low and exhibits a peaked behavior at about 30 K, which suggests either a multi-band electronic structure or an electron correlation effect in the system.

Facilities networks such as power system, transportation network and military network can be abstractly classified into multiplex networks. The study of multiplex networks disintegration is helpful to analyze the weaknesses of these networks, so as to improve the robustness of the networks.At present, the research on the disintegration of multiplex networks mainly focuses on the node-based attack strategy. However, the research results show that compared with the node-based attack, the edge-based attack can lead to larger cascading failure.In this paper, the optimal edge-based attack strategy in multiplex networks is studied and a combinatorial optimization model of optimal edge-based attack strategy in multiplex networks is constructed. Firstly, in this paper, the maximum eigenvalue of the network adjacency matrix is proposed as the network performance index reflecting the network information transmission ability. Secondly, a combinatorial optimization model of optimal edge attack strategy is proposed, and tabu search algorithm is introduced to solve the optimization model to obtain the optimal edge-based attack strategy. Finally, the disintegration effects of the optimal edge-based attack strategy and the baseline attack strategy are compared on the synthetic network model, and the optimality of the edge-based attack strategy based on the tabu search algorithm is verified.Our work provides a new approach for improving the robustness of infrastructure networks, which deserves further study.

Based on random phase approximation, we numerically calculate dynamical structure factors of a balanced two-dimensional (2D) Fermi superfluid, and discuss their energy, momentum and interaction strength dependence in the 2D BEC–BCS crossover. At a small transferred momentum, a stable Higgs mode is observed in the unitary 2D Fermi superfluid gas where the particle–hole symmetry is not satisfied. Stronger interaction strength will make the visibility of the dispersion of Higgs mode harder to be observed. We also discuss the dimension effect and find that the signal of the Higgs mode in two dimension is more obvious than that in 3D case. At a large transferred momentum regime, stronger interaction strength will induce the weight of the molecules excitation increasing, while in verse the atomic one decreasing, which shows the pairing information of Fermi superfluid. The theoretical results qualitatively agree with the corresponding quantum Monte Carlo data.