Omnidirectional reflection control of plane waves via giant magnetostrictive materials

The omnidirectional reflection behaviors of elastic waves and tuned by external magnetic fields are investigated. The projected band structures are used for analyzing omnidirectional reflection bands, which are also validated by the refraction spectra. It is demonstrated that omnidirectional reflection phenomenon can be efficiently tuned via the external magnetic field imposed on the Terfenol-D layer. Furthermore, an absolute band gap can be achieved by constructing two superlattices in tandem with different magnetic fields. Our design scheme and the modulation methodology open a new prospect for designing active acoustic mirrors and filters with high-quality.

Slater-Pauling-like Behavior of Spin Hall Conductivity in Pt-based Superlattices

The intrinsic spin Hall effect in the bulk systems of late transition metals (Os, Ir, Pt, and Au) as well as the Pt-based superlattices were investigated by using first-principle calculations. By comparing the computed spin Hall conductivities of Pt−M superlattices (M=Os, Ir, and Au) with different compositions and those obtained from atomic bulk composition, we saw that the spin Hall conductivities (SHCs) follow the behavior described by the Slater-Pauling curve, the maximum of which is at pure Pt bulk. From the examination of the band structures of the considered systems, we found that the origin of this behavior comes from the variation of the band structures as a direct consequence of the change of the number of electrons and hybridization effects.

Stability and electronic structure of magnesium hydride and magnesium deuteride under high pressure

Metal polyhydrides have attracted considerable attention because some of them become a metal under high pressure, and some undergo a phase transition into a superconductor. Some superconducting metal polyhydrides have recently been discovered with a high value of critical temperature (Tc) under pressure. In this research, we calculated the structures of MgH2, MgH3 and MgD3 under pressure between 0-300 GPa in order to determine the formation enthalpy and electronic property of their structures under high pressure by using density functional theory (DFT) based on the Quantum Espresso code. We found that the band structures reveal the metallic character of the compounds under high pressure. The energy band structures of MgHx and MgDx are exactly the same. However, their phonon dispersions are different due to the so-called isotope effect. We determined the composition stability by using the convex hull of Mg, H and the compounds. We found that MgH3 becomes thermodynamically more stable than MgH2 at around 150 GPa. The results of phonons confirm that they are dynamically stable. This finding is served as a basis for future superconducting calculations.

Engineering the Band Structures of Zigzag Blue Phosphorene and Arsenene Nanoribbons by Incorporating Edge Corrugations: A First Principles Exploration

Using first principles calculations, we have presented a short study on modulation of band structures and electronic properties of zigzag blue phosphorene (ZbPNR) and arsenene nanoribbons (ZANR) by etching the edges of NRs. We have taken the width of both NRs as N = 8 and corrugated the edges in a cosine-like manner. Optimizing every structure and further investigating their stabilities, it was seen that both the etched NRs are energetically feasible. From the computed band structures, the band gaps were seen to be increased for both the NRs on increasing number of etched layers and direct gap semiconductor nature was recorded. Highest energy gap observed were 2.26 and 2.41 eV for ZbPNR and ZANR, respectively. On further application of electric field, we observed the very interesting semiconductor-to-metallic property transition which was explained by wave function plots. Being elements of same group, a similar trend of band gaps modulations was observed for both NRs. This fascinating method of electronic property tuning of the studied NRs can be useful in various nanoscale electronic applications.

Band structures and topological properties of twisted bilayer MoTe2 and WSe2

We calculate the electronic band structures and topological properties of twisted homobilayer transition metal dichalcogenides(t-TMDs), in particular, bilayer MoTe2 and WSe2 based on a low-energy effective continuum model. We systematically show how the twist angle, vertical electric field and pressure modify the band structures of t-TMDs, often accompanied by topological transitions.We find the variation of topological transitions mainly take place in a limited range of parameters. The electric field can efficiently tune the energy of the topmost second valence band to motify the Chern numbers of the topmost three valance bands. The topological property of the topmost first valance band can be modified by electric field and pressure, but doesn’t depend on twist angle. We show the band gap between the topmost second and third valance bands that both change from non-trivial to trivial closes at κ − -point of the moiré Brillouin zone.

Structural Analysis, Phase Stability, Electronic Band Structures, and Electric Transport Types of (Bi2)m(Bi2Te3)n by Density Functional Theory Calculations

Thermoelectric power generation is a promising candidate for automobile energy harvesting technologies because it is eco-friendly and durable owing to direct power conversion from automobile waste heat. Because Bi−Te systems are well-known thermoelectric materials, research on (Bi2)m(Bi2Te3)n homologous series can aid the development of efficient thermoelectric materials. However, to the best of our knowledge, (Bi2)m(Bi2Te3)n has been studied through experimental synthesis and measurements only. Therefore, we performed density functional theory calculations of nine members of (Bi2)m(Bi2Te3)n to investigate their structure, phase stability, and electronic band structures. From our calculations, although the total energies of all nine phases are slightly higher than their convex hulls, they can be metastable owing to their very small energy differences. The electric transport types of (Bi2)m(Bi2Te3)n do not change regardless of the exchange–correlation functionals, which cause tiny changes in the atomic structures, phase stabilities, and band structures. Additionally, only two phases (Bi8Te9, BiTe) became semimetallic or semiconducting depending on whether spin–orbit interactions were included in our calculations, and the electric transport types of the other phases were unchanged. As a result, it is expected that Bi2Te3, Bi8Te9, and BiTe are candidates for thermoelectric materials for automobile energy harvesting technologies because they are semiconducting.