We present evidence of topological surface states in β-Ag2Te through first-principles calculations, periodic quantum interference effect and ambipolar electric field effect in single crystalline nanoribbon. Our first-principles calculations show that β-Ag2Te is a topological insulator with a gapless Dirac cone with strong anisotropy. To experimentally probe the topological surface state, we synthesized high quality β-Ag2Te nanoribbons and performed electron transport measurements. The coexistence of pronounced Aharonov-Bohm oscillations and weak Altshuler-Aronov-Spivak oscillations clearly demonstrates coherent electron transport around the perimeter of β-Ag2Te nanoribbon and therefore the existence of topological surface states, which is further supported by the ambipolar electric field effect for devices fabricated by β-Ag2Te nanoribbons. The experimental evidences of topological surface states and the theoretically predicted anisotropic Dirac cone of β-Ag2Te suggest that the material may be a promising candidate of topological insulator for fundamental study and future spintronic devices.

The low-rate DoS (LDoS) attack is a new kind of network attack which has the characteristics such as low speed and good concealment. The software defined network, as a new type of network architecture, also faces the threat from LDoS attacks. In this article, we propose a detection method of LDoS attacks based on a hybrid deep learning model CNN-GRU: the convolutional neural network (CNN) and the gated recurrent unit (GRU). First, we extract field values such as n_packets and n_bytes, from the flow rule, and construct the average numbers of packets and bytes as the input data of the hybrid model. Then, to enhance the detection performance of the hybrid model, we improve the sailfish algorithm to optimize the hyperparameters of CNN and GRU automatically in the training process. Finally, we adopt hyperparameter optimized CNN and GRU to extract deeper spatial and temporal features of input data, respectively, which achieves accurate detection of the LDoS attack. The experimental results demonstrate that the proposed hybrid deep learning model-based method outperforms other traditional machine learning algorithms in terms of detection efficiency and accuracy.

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The Cs2SnX4 (X = Cl, Br, and I) halide perovskites are currently emerging as a new family of 2D materials and promising candidates for photovoltaic and optoelectronic devices. Herein, the structural, electronic, and optical properties of the Cs2SnX4 multilayers (Ms) with 1–3 layers are investigated by density functional theory (DFT). The structural properties show that the bond length variation of Cs2SnX4 is closely related to surface effects. The Cs2SnCl4 Ms have the lowest formation energies and the best stability, and the formation energies decrease and the stability improves when the number of layers increases. The electronic properties show that the direct‐bandgap semiconductor Cs2SnX4 Ms bandgap values (Cl: 1.513–1.188–0.932, Br: 1.342–1.015–0.862, I: 1.198–0.903–0.729) decrease with the change from 1 to 3 layers and from Cl to I. The p orbitals of X atoms and 5p orbitals of Sn atoms are mainly involved in conduction. The optical properties indicate that Cs2SnX4 Ms achieve coverage and adjustability in the near‐infrared and visible‐light ranges. The calculations provide a fundamental theoretical basis for the research and application of Cs2SnX4.

CsPbX3 inorganic perovskites have gained widespread attention due to the excellent stability and interesting properties. This article focuses on the exciton properties of CsPbBr3 with different layer numbers. The electronic and optical properties are also investigated. The distribution of excitons (electrons and holes) is closely related to the density of states near the bottom of the conduction band and the top of valence band. Based on potential analysis, it is found that the excitons are affected by the bromine atoms. With increasing thickness, the bandgap decreases and the absorption spectrum that appears obviously in the bandgap moves to lower energy, the maximum binding energy of bright excitons becomes smaller, and the corresponding Bohr radius becomes larger. These results provide a theoretical basis for the theoretical and experimental studies of CsPbBr3 and provide some guidance for the design of optoelectronic devices.