Ideal Hopf-link mode in phonon material Ba2OsH6

Abstract

Phonon systems have emerged as potential platforms for exploring nontrivial band topologies. Meanwhile, two (or more) closed nodal lines (CNLs) may nest with each other and form a Hopf-link mode in momentum space. However, nontrivial Hopf-link modes in phonon systems have yet to be reported in realistic materials. In this work, based on the first principles calculations and symmetry analysis, we predict the presence of the clean Hopf-link mode in a phonon material, namely Ba _2 OsH _6 . Specifically, two CNLs around X ( X’ ) point hook each other and form a Hopf-link configuration, which is protected by two perpendicular mirror planes. More importantly, the Hopf-link mode exhibits the drumhead-like surface states. This work presents a potential candidate for exploring Hopf-link mode in spinless systems and provides a way to understand the unique geometry of CNLs.

Keywords

• Hopf-link
• topological phonons
• first-principles calculations