Facile mechanism to induce topological transition in MXene

We have investigated the electronic structure of the Sc ₂ C(OH) ₂ MXene interfacing with a polar AlN multi-layer or a hydrogenated AlN surface. Density functional theory calculations reveal that the nearly free electron (NFE) states of the MXene shift down when the MXene is in contact with a polar flat surface. The Sc ₂ C(OH) ₂ /AlN heterostructure shows a Dirac cone and inversion in the band structure. The H-s, Sc-d, and C-p orbitals are involved in the band-inversion. The electronic structure of Sc ₂ C(OH) ₂ /AlN heterostructure is found to be topological since the topological invariant Z ₂ =1. We suggest that a band inversion can be induced by contacting with any flat insulating polar surface that has no excess surface-charge. However, it is crucial that the MXene surface is not perturbed (e.g., by dangling bonds). As a proof of concept, we have investigated the electronic structure of Sc ₂ C(OH) ₂ adsorbed on a hydrogenated AlN surface and observed band inversion. The band dispersions of the adsorbed MXene are reminiscent of a Weyl semi-metal. The adsorption on a polar material is a facile method to induce a topological electronic structure in the Sc ₂ C(OH) ₂ MXene, which may be utilized in various device applications.