Bilayer phosphorene attracted considerable interest, giving a potential application in nanoelectronics owing to its natural bandgap and high carrier mobility. However, very little is known regarding the possible usefulness in spintronics as a quantum spin Hall (QSH) state of material characterized by a bulk energy gap and gapless spin-filtered edge states. Here, we report a strain-induced topological phase transition from normal to QSH state in bilayer phosphorene, accompanied by band-inversion that changes number from 0 to 1, which is highly dependent on interlayer stacking. When the bottom layer is shifted by 1/2 unit-cell along zigzag/armchair direction with respect to the top layer, the maximum topological bandgap 92.5 meV is sufficiently large to realize QSH effect even at room-temperature. An optical measurement of QSH effect is therefore suggested in view of the wide optical absorption spectrum extending to far infra-red, making bilayer phosphorene a promising candidate for opto-spintronic devices.

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Seven types of arsenenes and antimonenes with their band structures and partial densities of states.

Recently, all-inorganic perovskite quantum dots have become a hot research topic due to their unique optical response. We have studied barium titanate quantum dots and their hybrid structure consisting silver (Ag) nanowires interacting with ultrafast laser pulses based on time-dependent density functional theory (TDDFT). Through controlling the wavelength and intensity of incident ultrafast light pulses, insulator–metal transition and long-wavelength plasmons can be induced in barium titanate quantum dots. This is because localized field effect breaks the bonds between surrounding oxygen atoms and barium atoms, thus creating metallic patches to form photocurrents. In addition, our results elucidate that Ag nanowires can improve the ultrafast optical responsivity of barium titanate quantum dots especially in the infrared region. Our work theoretically broadens the cognition of all-inorganic perovskite quantum dots interacting with laser and reveals that inorganic perovskite quantum dots have great potential in future applications of optoelectronic devices.

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Recently, all-inorganic perovskite nanostructures have become a hot research topic due to their unique optical response and novel properties. Here, we theoretically study the optical response in Cs 2 PbX 4 and CsPb 2 X 5 (X = Cl, Br, and I) nanostructures.First, to study the ground state, we calculate the band structures of the periodic system using the HSE06 method, which shows that all those periodic perovskites possess the direct band gaps, with distribution from 2.225 to 3.536 eV. Their valence band maximum are mainly contributed from both halogen and lead atoms, while the conduction band minimum are mainly contributed from lead atoms. Then, we study the excited state using the time-dependent density functional theory method and find that, with the increase of halogen atom radius, the photogenerated carrier concentrations in perovskite nanostructures become larger, while the surface plasmon resonance becomes localized rather than long-range. Moreover, through the analysis of photocurrent and local field enhancement, Cs 2 PbX 4 and CsPb 2 X 5 nanostructures exhibit nearly 40 μA photocurrent along the direction of optical polarization. Besides, by regulating the different anions, we predict that field enhancement in Cs 2 PbI 4 and CsPb 2 I 5 share a much stronger distribution at both the center and border parts of Pb-I planes due to localized plasmon resonance, while other perovskites are distributed at the edge parts of Pb-I planes, caused by long-range plasmon resonance. Our research shows that all-inorganic perovskite nanostructures are great candidate materials for developing optoelectronic devices working in high-frequency and high-energy regions and improving their application in sensitive detection and sensors.