Browsing by Author "Evangelista, Igor"
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Item Large Rashba spin splittings in bulk and monolayer of BiAs(Physical Review Materials, 2024-05-20) Zubair, Muhammad; Evangelista, Igor; Khalid, Shoaib; Medasani, Bharat; Janotti, AndersonThere is great interest in developing new materials with Rashba split bands near the Fermi level for spintronics. Using first-principles calculations, we predict BiAs as a semiconductor with large Rashba splitting in bulk and monolayer forms. Bulk BiAs has a layered crystal structure with two atoms in a rhombohedral primitive cell, derived from the structure of the parent Bi and As elemental phases. It is a narrow band gap semiconductor, and it shows a combination of Rashba and Dresselhaus spin splitting with a characteristic spin texture around the L point in the Brillouin zone of the hexagonal conventional unit cell. It has sizable Rashba energies and Rashba coupling constants in the valence and conduction bands at the band edges. The 2D monolayer of BiAs has a much larger band gap at Γ, with a circular spin texture characteristic of a pure Rashba effect. The Rashba energy and Rashba coupling constant of monolayer BiAs are large compared to other known 2D materials and rapidly increase under biaxial tensile strain.Item Structural Phase Transitions between Layered Indium Selenide for Integrated Photonic Memory(Advanced Materials, 2022-04-18) Li, Tiantian; Wang, Yong; Li, Wei; Mao, Dun; Benmore, Chris J.; Evangelista, Igor; Xing, Huadan; Li, Qiu; Wang, Feifan; Sivaraman, Ganesh; Janotti, Anderson; Law, Stephanie; Gu, TingyiThe primary mechanism of optical memoristive devices relies on phase transitions between amorphous and crystalline states. The slow or energy-hungry amorphous–crystalline transitions in optical phase-change materials are detrimental to the scalability and performance of devices. Leveraging an integrated photonic platform, nonvolatile and reversible switching between two layered structures of indium selenide (In2Se3) triggered by a single nanosecond pulse is demonstrated. The high-resolution pair distribution function reveals the detailed atomistic transition pathways between the layered structures. With interlayer “shear glide” and isosymmetric phase transition, switching between the α- and β-structural states contains low re-configurational entropy, allowing reversible switching between layered structures. Broadband refractive index contrast, optical transparency, and volumetric effect in the crystalline–crystalline phase transition are experimentally characterized in molecular-beam-epitaxy-grown thin films and compared to ab initio calculations. The nonlinear resonator transmission spectra measure of incremental linear loss rate of 3.3 GHz, introduced by a 1.5 µm-long In2Se3-covered layer, resulted from the combinations of material absorption and scattering.