Intrinsic nontrivial topology and van Hove singularities in superconductors YX2Si2 (X=Ni, Rh)

Abstract

Searching for nontrivial topology in superconductors is one of reasonable strategies to realize topological superconductor. Based on first-principles calculation, we have studied electronic structures and topological properties of ThCr₂Si₂ type ternary superconductors YX₂Si₂ (X=Ni, Rh) which have the same crystal structure as iron-based superconductors CaFe₂As₂. For material YNi₂Si₂, the topological Dirac cone locates below Fermi level 0.61 eV on (001) surface. By substituting Rh atoms for Ni atoms, the $d_{xy}$ orbital of transition metal atom Rh is lifted up above the Fermi level. This variation of band structure is responsible for topologically nontrivial surface states and van Hove singularities (vHs) in the vicinity of the Fermi level of superconductor YRh₂Si₂. The density of states (DOS) peak near Fermi level implies the existence of strong electron correlation which may induce unconventional superconductivity. The natural combination of topology and superconductivity in these materials provides us a new platform to discuss topological superconductor and mechanism of superconductor.