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Single-domain formation of SrMnBi2 films on polar LaAlO3 substrate

By considering the crystal symmetry of the Dirac semimetal candidate SrMnBi2, it is expected that a substrate based on a square lattice is preferred to form a single-domain growth of a thin film. In this study, however, we observed different schemes of interface formation of SrMnBi2 using molecular-beam epitaxy on two oxide substrates of SrTiO3(001) and LaAlO3(001), both of which are often applied to the growth of the films with square lattices. Although antiphase domains appear in the SrMnBi2 film on SrTiO3(001), a single domain develops on LaAlO3(001) with an abrupt interface. The distinct difference indicates that the surface of the LaAlO3(001) substrate plays a crucial role in the selection of the initial growth plane. Judging from the abrupt interface image in scanning transmission electron microscopy and the four-fold symmetric in-plane x-ray diffraction pattern representing the orientation relationship of SrMnBi2 film [110]//LaAlO3 [100], the polar surface termination with (AlO2)− or (LaO)+ probably promotes the interface formation of the ionic Sr or Bi plane on the surface, respectively. According to the semimetallic electronic structure of SrMnBi2, the electrical transport properties of the films can be consistently evaluated by the two-carrier model with high-mobility electrons and low-mobility holes. Our demonstration of the single-domain growth of the Dirac semimetal provides a key technique toward the future engineering of heterostructures composed of topological materials.