DFT insights into surface properties of anti-perovskite 3D topological crystalline insulators: A case study of (001) surfaces of Ca3SnO

Structure inversion asymmetry enhanced electronic structure and electrical transport in 2D A3SnO (A = Ca, Sr, and Ba) anti-perovskite monolayers

“…and pulsed laser deposition (PLD) techniques for the synthesis of A 3 SnO thin films on various substrates indicate that (001)oriented surfaces are experimentally achieved showing metallic character [44,58,60,61]. These results also agree well with density functional theory (DFT) based first-principles calculation for the (001) surface [62][63][64]. Interestingly, it has become evident that manipulating the inversion symmetry in A 3 SnO can significantly impact the evolution of the surface electronic structure [64].…”

“…The values for Ca 3 SnO-ML, Sr 3 SnO-ML, and Ba 3 SnO-ML are found to be 0.942, 0.751, and 0.551 J/m 2 , respectively, which are all = 1.206 J/m 2 which we have computed as a benchmark in the present work using the same procedure for a fully optimized 1 UC thick SrTiO 3 -ML. Moreover, of the studied ML systems are considerably smaller than surface energies of A 2 Otermianted and ASn-terminated (001) surfaces of bulk A 3 SnO [62,63]. It is interesting to note that for both asymmetric perovskite as well as anti-perovskite MLs decreases with increasing roughness of the surface (as discussed later).…”

“…Interestingly, it has become evident that manipulating the inversion symmetry in A 3 SnO can significantly impact the evolution of the surface electronic structure [64]. Since A 3 SnO surfaces in thin films are constructed by stacking [A 2 O] 2+ and [ASn] 2− layers along [001] direction, a net dipole moment perpendicular to the (001) would bring about an electronic reconstruction that gives rise to metallic states [62][63][64]. For the case of symmetric surface terminations (i.e., A 2 O-terminated or ASn-terminated) studied for the bulk A 3 SnO, electrons or holes from the bulk-like middle layer are available for electronic reconstruction to compensate for the polar catastrophe [64][65][66].…”

“…1(b)), the resulting space group #99 (P4mm) lacks mirror symmetry as well as spatial inversion symmetry along the [001] direction. On the contrary, for a symmetric A 2 O-terminated slab of anti-perovskites A 3 SnO [62][63][64], both the inversion and mirror symmetries along [001] crystallographic direction are intact for the space group #123 (P4/mmm). Therefore, an opening of the band gap at the 2D limit may only be realized for the asymmetric MLs of A 3 SnO.…”