Orbital-Spin Texture and Landau Levels in Two-Dimensional Rashba-Dirac Lead Chalcogenides
This event is part of the Preliminary Oral Exam.
Examining committee: David Campbell, Harold Park, So-Young Pi, Anna Swan
Abstract: We study two-dimensional lead chalcogenides PbX (X=S, Se, Te) using first-principles based on density functional theory framework. Due to the heavy Pb element with strong spin-orbit coupling (SOC) and the broken inversion symmetry of its buckled monolayer structure, PbS is found to possess Rashba-Dirac cone with a relatively large Rashba parameter at Γ and M point of λ~1eV/Å and λ~5eV/Å, respectively, which are comparable to other giant Rashba materials (e.g BiTeBr). We develop a new tight-binding formulation to describe the band structure, orbital texture, and spin texture. SOC mixes the out-of-plane and in-plane orbital components of atoms with same species while the inversion symmetry breaking (degree of buckling) mixes the out-of-plane and in-plane orbitals of atoms with different species. The latter can be controlled via applications of in-plane strains allowing control of spin splitting and texture as well as Fermi velocity at Γ and M. The novel property of PbX with unique and tunable orbital and spin texture, which has not been found before in free-standing two-dimensional materials, opens a new way of utilizing two-dimensional materials for next-generation electronic devices. Lastly, based on our tight-binding results, we will discuss the effect of external magnetic field and Landau levels in Rashba-Dirac materials