Design of Sn-doped cadmium chalcogenide based monolayers for valleytronics properties

Abstract

Valleytronics has emerged as an interesting field of research in two-dimensional (2D) systems and uses the valley index or valley pseudospin to encode information. Spin–orbit coupling (SOC) and inversion symmetry breaking lead to spin-splitting of bands near the valleys. This property has promising device applications. In order to find a new 2D material useful for valleytronics, we have designed hexagonal planar monolayers of cadmium chalcogenides (CdX, X = S, Se, Te) from the (111) surface of bulk CdX zinc blende structure. The structural, dynamic, mechanical and thermal stability of these structures is confirmed. A band structure study reveals valence band local maxima (valleys) at the K and K′ symmetry points. The application of SOC initiates spin-splitting in the valleys that lifts the energy degeneracy and shows strong valley–spin coupling. To initiate stronger SOC, we substituted two Cd atoms in the almost-planar monolayers with Sn atoms, which increases the spin-splitting significantly. Zeeman-type spin-splitting is observed in the valley region and Rashba spin-splitting is observed at the Γ point for Sn-doped CdSe and CdTe monolayers. Berry curvature values are higher in all the Sn-doped monolayers than in the pristine monolayers. These newly designed monolayers are thus found to be suitable for valleytronics applications. Sn-doped monolayers show band inversion deep in the valence and conduction bands between Sn s and p and X p states but lack topological properties.