First Principles Studies of Topological Insulating Behavior in Lanthanum-Monopnictides and their Heterostructures

Abstract

The topological insulating behavior of LaX (X = Bi, Sb, As, and P) and their heterostructure combinations are investigated. The system's bulk-band-inversion is analyzed, and the (Formula presented.) -topological indexes are calculated using LDA and mBJLDA exchange functionals. Strong topological insulating behavior in LaBi is confirmed from bulk band inversion. Linearly dispersive Dirac-cone in the (001)-surface band structure is observed. The other LaX binaries also exhibit bulk-band-inversion under LDA+SOC settings but disappear after including the mBJ potential. The robustness of the surface Dirac cone is tested by estimating the surface band structure under uniaxial strain. The result shows that Dirac-cone in the (001)-surface is unaltered only for the LaBi system and destroyed in all other three binaries, concluding the topologically trivial nature of LaP, LaSb, and LaAs. The investigation is further extended to study the multilayer LaX<inf>1</inf>/LaX<inf>2</inf> systems composed of an alternate stacking of two different LaX binaries. The findings suggest that the multilayer structures exhibit topological insulating behavior only when LaBi is present in the system. Bulk-band-inversion and surface Dirac-cone structures in LaBi/LaAs, LaBi/LaSb, and LaBi/LaP multilayers are observed. Furthermore, the surface Dirac cones remain unchanged under the influence of TR-preserving perturbation, confirming these systems possess strong topological insulating character. © 2023 Wiley-VCH GmbH.