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 leads 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. Band structure study reveals valence band local maxima (valleys) at K and K′ symmetry points. Application of SOC initiates spin-splitting in the valleys that lifts the energy degeneracy and shows strong valley-spin coupling character. To initiate stronger SOC, we have substituted two Cd atoms in the almost planar monolayers by 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 more in all the Sn-doped monolayers than 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.