Topological Properties Of Stacked Carbon Thin Film Materials

Carbon element has a large number of allotropes due to its rich and diverse hybrid forms.Especially since graphene was successfully prepared in 2004,carbon thin film materials have sprung up like mushrooms.These carbon thin film materials exhibit strange physical and chemical properties.On the other hand,topological materials are currently hot research topics in the field of condensed matter physics,and various topologies have been proposed one after another.For example,zero-dimensional nodal points,one-dimensional nodal lines,and two-dimensional nodal surfaces.Although some two-dimensional thin-film materials also have topological properties,compared with three-dimensional materials,their dimensions severely limit the possibility of some complex topological phases appearing in two-dimensional thin-film materials.For example,nodal chains and nexus points cannot appear in two-dimensional materials.In order to break through the limitation of dimensionality on topological phases and expand the application of carbon thin film materials,we design topological materials and find new topological phases by stacking carbon thin film materials,and study their topological properties.In this paper,a combination of first-principles calculation and tight-binding approximation method is proposed to achieve a series of critical topological phases based on Kagome lattices,such as critical nodal point,critical nodal lines or nodal rings.After breaking the C₃ rotational symmetry of the Kagome lattice,the quadratic nodal point splits into two critical nodal points.By stacking a single layer of Kagome lattice into a three-dimensional layered structure,a critical nodal line or nodal ring can be obtained.In addition,we use Kagome graphene as an example to illustrate that these critical topological phases could be realized in real materials.We found that when a hole doping into the structure,these Dirac-type topological phases will transform Weyl-type topological phases.In addition,based on a two-band effective model with PT symmetry,it is proposed that two different types of nodal lines or nodal rings can be obtained by stacking two-dimensional Dirac film materials.When an external strain is applied,the two-type topological nodal lines are very different,the evolution of the topological phase of one type of nodal line occurs on the mirror symmetry,and the evolution of the topological phase of the other type of nodal line is in the three-dimensional momentum space Rotates around a certain axis.We take 6,6,12-graphyne as an example to show that these two phases can be realized in the material.In addition,the tight-binding model was used to fit the energy bands of single layer 6,6,12-graphyne and its two materials to illustrate the evolution of its topological phase.Our results indicate that one can stack existing thin-film materials into three-dimensional layered materials to find new topological phases.Our work combines two popular areas of topological materials and 2D thin film materials,paving the way for designing and finding new topological materials by stacking 2D thin film materials.