Topological Phase Transition Induced By Image Potential States In Mxenes: A Theoretical Investigation

MXenes material is a two-dimensional material composed of two-dimensional transition metal carbides and nitrides,which has a lot of tunable physical and chemical properties.In the electronic and energy storage equipment,their prospects are diversified and have a lot of excellent properties,such as good conductivity,short ion transport path,large specific surface area,strong stability,etc.,which makes people have a great interest in the scientific research of MXenes materials.During the study,it was found that MXenes materials could be functionalized by different surface ends,and some O and F functionalized MXenes monolayers were predicted to be topological insulators.However,the MXenes monolayers of OH functional groups to be studied are rare,so their electronic structures need to be studied in more detail.The results show that the OH functional group can significantly reduce the work function of MXenes material,and then the mirror state of the material will be relatively close to the Fermi level,and will move like the Fermi level.The wave functions of these mirror states are wide on the outer surface space.Because the overlap and hybridization effects of the wave functions between adjacent layers are significant,the energy of the mirror state can be controlled by adjusting the distance between the layers by stacking the OH-functionalized MXenes material.In this case,these stacked layers are interacting and coupled to the mirror state.The electronic properties of individual OH-MXenes monolayers are different from those of their stacked multilayers.In order to emphasize the important role of mirror state in controlling the topological properties of materials,we have studied a group of hypothetical MXenes materials of M'₂M''C₂(OH)₂,where M'refers to V,Nb,Ta,and M''refers to Ti,Zr,Hf.Fundamental first-principles calculations show that both their valence bands and conduction bands are from the mirror state,which proves that the band band of OH-Mxenes monolayers is topologically trivial.However,by stowing,it can be shown that OH-Mxenes multilayer materials may become nontopological materials.In other words,the topological properties of laminated multilayers depend on the distance between layers.The method involving energy band inversion proposes the mirror state.Our results are valid not only for MXenes,but also for any material whose mirror states have energies close to the Fermi level.The main content of this paper includes the following points:1.First-principles calculations based on density functional theory were used to study the stacking of superposed OH functionalized MXenes materials.2.Establish the wave function of mirror state,and study the effect of interlayer distance on electronic structure by studying the properties of wave function.3.By changing the layer spacing,the mirror states can be adjusted to affect the topological properties of OH-MXenes laminated multilayer films.