Kramers nodal line in the charge density wave state of YTe_3 and the influence of twin domains

Recent studies have focused on the relationship between charge density wave (CDW) collective electronic ground states and nontrivial topological states. Using angle-resolved photoemission and density functional theory, we establish that YTe_3 is a CDW-induced Kramers nodal line (KNL) metal, a newly proposed topological state of matter. YTe_3 is a non-magnetic quasi-2D chalcogenide with a CDW wave vector (q_ cdw) of 0.2907c^*. Scanning tunneling microscopy and low energy electron diffraction revealed two orthogonal CDW domains, each with a unidirectional CDW and similar YTe_3. The effective band structure (EBS) computations, using DFT-calculated folded bands, show excellent agreement with ARPES because a realistic x-ray crystal structure and twin domains are considered in the calculations. The Fermi surface and ARPES intensity plots show weak shadow bands displaced by q_ cdw from the main bands. These are linked to CDW modulation, as the EBS calculation confirms. Bilayer split main and shadow bands suggest the existence of crossings, according to theory and experiment. DFT bands, including spin-orbit coupling, indicate a nodal line along the Σ line from multiple band crossings perpendicular to the KNL. Additionally, doubly degenerate bands are only found along the KNL at all energies, with some bands dispersing through the Fermi level.