The First Principle Study Of Weyl Semimetal YCoC₂

the study of electronic structure topology of crystalline materials has emerged in the past decade as a major new theme in modern condensed matter physics.the starting point is the remarkable discovery of topological insulator,the focus has recently shift to the topological semimetal since the burst of topological materi-als.The Weyl semimetal is a special one among the topological semimetals,we use the effective hamiltonian H_w=??? to describe the physical properties of Weyl fermion,where ??? is the pauli matrix,??? means the crystal momentum,and the fermi velocity?defines the chirality of the two kinds of Weyl fermion.In this thesis,we mainly discuss the Weyl semimetals.In the first part of this thesis,The frame work of the numerical methods commonly used in this article is introduced.The computational methods is divided into two parts,the first principle method based on density functional theory,the second part is the physical analysis methods based on the wannier Hamiltonian constructed by wannier90.The main work is the application of these two physical tools.Based on first principles calculations,we propose that a nonmagnetic material Y CoC₂without inversion symmetry is a Weyl semimetal including both type-I and type-II band dispersions,in the absence of spin-orbit-coupling?SOC?,there exists a node ring in the momentum space protected by mirror invariant plane.in the presence of SOC,the node ring is gapped and ten pairs of weyl points emerge.Fermi arc surface states are observed both on?001?and?100?surface.This material offers a convenient platform to explore the intriguing physics of coexistence of type-I and type-II weyle fermions.