Unusual Janus BiTeSe Topological Insulators Displaying Second-Harmonic Generation, Linear-in-Temperature Resistivity, and Weak Antilocalization.

Well-established knowledge about inversion-symmetric BiTeSe topological insulators characterizes the promising new-generation quantum device. Noticeably, the inversion asymmetric phase containing different surface electronic structures may create an extra topological phenomenon pointing to a new device paradigm. Herein, Janus BiTeSe single-crystal nanosheets with an unconventional stacking sequence of Se-Bi-Se-Bi-Te are realized via chemical vapor deposition growth, which is clarified by atomically resolved AC-STEM and elemental mapping.

Ambient-Pressure Recoverable Polynitrogen Solids Assembled by Pentazolate Rings with High Energy Density.

Crystal structure predictions and first-principles calculations were used to predict three polynitrogen solids (8-N, 12-N, and 24-N) that possess competitive enthalpies as compared to the synthesized open-chain N phase at pressures in the range of 0-60 GPa. 8-N, 12-N, and 24-N contain edge-shared, N-linked, and N-bridged pentazolate rings and form molecular N, molecular N, and quasi-one-dimensional N ribbons, respectively. The calculations of formation enthalpies show that the three polynitrogen solids can be synthesized by compressing cyclo-N salts in hydrogen-saturated environments.

Two-dimensional SiS with a negative Poisson's ratio and promising optoelectronic properties.

Two-dimensional materials with a negative Poisson's ratio, known as auxetic materials, are of great interest owing to their improved mechanical properties, which enable plenty of advanced nanomechanical devices. Here, by first-principles swarm-intelligence structural search methods, we predict a thermodynamically stable SiS monolayer, which has a puckered 2D lattice in which the S atoms are adsorbed on the top of a distorted tetragonal silicene layer. The puckered 2D lattice makes the SiS monolayer exhibit in-plane negative Poisson's ratios of -0.

A BN monolayer: a direct band gap semiconductor with high and highly anisotropic carrier mobility.

Two-dimensional materials with a planar lattice, suitable direct band gap, and high and highly anisotropic carrier mobility are desirable for the development of advanced field-effect transistors. Here we predict three thermodynamically stable B-rich 2D B-N compounds with the stoichiometries of BN, BN, and BN using a combination of crystal structure searches and first-principles calculations. Among them, BN has an ultraflat surface and consists of eight-membered BN and pentagonal BN rings.