Local Symmetry Broken Induced by Cr on the Surface of Two-Dimensional Cr2Te3 System

Transition metal chalcogenide Cr₂X₃ (X=S, Se, Te) have similar trigonal crystal symmetry but possess diverse electronic and magnetic properties [1]. Cr₂S₃ behaves as ferrimagnet semiconductor, Cr₂Se₃, a half metal spin-glass, and Cr₂Te₃, a ferromagnetic metal. It is, therefore, interesting to examine how the local symmetry is broken when such systems are down to ultrathin structures and how such effect influences their electronic and magnetic properties. Our preliminary DFT study on ultrathin Cr₂Te₃ films with different thickness (e.g., 1L-3L) and termination (e.g. Te/Te, Cr/Te, Cr/Cr) has shown that Cr atoms at the surface play a key role in breaking local symmetry. For instance, the Te-Te termination results in a strong horizontal compression and vertical expansion (comparing with bulk) with all Cr possessing centrosymmetric bonding nature, while the Cr-Te termination causes a weak horizontal compression and vertical expansion with local bonding symmetry broken on all Cr. However, the Cr-Cr termination leads to a vertical compression and a weak horizontal expansion with most Cr changing to non-centrosymmetric bonding nature, associated with a transition from metallic to half metallic feature, providing a termination engineering on the electronic properties of Cr₂Te₃films.