Drumhead surface states and topological nodal-line fermions in TlTaSe2

Abstract

A topological nodal-line semimetal is a new state of matter with one-dimensional bulk nodal lines and two-dimensional “drumhead” surface bands. Based on first-principles calculations and our effective k · p model, we theoretically propose the existence of topological nodal-line fermions in the ternary transition-metal chalcogenide TlTaSe2. The noncentrosymmetric structure and strong spin-orbit coupling give rise to spinful nodal-line bulk states which are protected by a mirror reflection symmetry of this compound. This is remarkably distinguished from other proposed nodal-line semimetals such as Cu3NPb(Zn) in which the nodal line exist only in the limit of vanishing spin-orbit coupling and thus is not possible in real material. We show that the “drumhead” surface states in TlTaSe2, which are associated with the topological nodal lines, exhibit an unconventional chiral spin texture and an exotic Lifshitz transition as a consequence of the linkage among multiple “drumhead” surface-state pockets, suggesting a new type of 2D topological metal.