No abstract

No abstract

Topological materials are considered as a novel quantum state of matter, which can be characterized by symmetry-protected Dirac interfacial states, and exhibit an exotic phenomenon when combined with the other phases. The topological phase in the perovskite structures is important since it can provide various heterostructure interfaces with multifunctional properties. Alpha-(α-) phase cesium-based halide perovskites CsSnX3 (X = I, Br, Cl) can be considered as a promising candidate for topological semiconductors under hydrostatic pressures. The narrow bandgap of these compounds (≤1.83 eV) has made them interesting materials for the electronic, optoelectronic, and photovoltaic applications. In the current research, we systematically carry out first-principles density functional theory (DFT) to study the effects of hydrostatic pressure on the electronic structure of CsSnX3 (X = I, Br, Cl) compounds. The topological phase of these compositions is investigated using the Fu–Kane and Wilson loop methods in order to identify the Z2 topological invariants for each structure. The topological surface states (TSSs) of the (001) plane of these compounds are investigated using the semi-infinite Green's function. These TSSs guarantee the nontrivial nature of CsSnX3 compounds under pressure. With respect to the engineering applications, three important mechanical properties of these compounds including elastic anisotropy, ductility, and hardness are also investigated.

No abstract

Topological insulators with novel surfaces or edge states are the topological nature sequel of bulk electronic wave functions of these materials. The observed signatures in the electronic structure of topological insulators can make them excellent candidates for thermoelectric materials. Low dimensional materials such as phosphorene and Bi 2 Te 3 nanowire have been confirmed to be desirable for the design of devices with high thermoelectric performance. So in this work, the phonon modes, formation energy and cohesive energy of LaX (X = Sb, Bi) monolayers are first calculated and investigated. Then the band order of these monolayers is investigated by the band structure calculations and the topological phase of these monolayers is proved by using the calculation of Z 2 topological invariant. The energy band gap and the band inversion strength of these monolayers are evaluated under in-plane strains. Also, the effect of different temperatures and in-plane strains on the thermoelectric performance of LaX monolayers is studied. The results show the high thermoelectric efficiency and d-p topological band inversion of these monolayers under compressive strains.