Spectroscopic evidence of ideal Kramers nodal line metals in an intercalated transition metal dichalcogenide family

Acting as a Dirac solenoid concentrating Berry curvature along one-dimensional lines connecting time reversal invariant momenta in the k-space, Kramers nodal line (KNL) has been recently predicted [1] and demonstrated by bulk sensitive soft x-ray angle-resolved photoemission spectroscopy (ARPES) in the paramagnetic phase of SmAlSi [2]. However, there are only scarce experimental examples of ideal KNL metal where the Kramers nodal lines cross the Fermi level. Here using ARPES, spin-ARPES, circular dichroism ARPES, and first-principles calculations, we demonstrate the existence and spin texture of the KNL state in three isostructural intercalated transition metal dichalcogenide compounds, a material family also showing superconductivity and charge density waves at lower temperatures. Such KNL state can also be tuned into Kramers Weyl fermions under uniaxial strain. Our results suggest a promising alternative platform for realizing Weyl fermion related optical and (magneto-)transport phenomena and exploring correlated topology.