Magnetic-direction tunable Weyl line in A-A stacking kagome magnet*

Kagome magnets provide a fascinating platform for realizing a plethora of exotic topological orders, such as Chern insulator, magnetic Weyl and nodal line semimetals, which depend on the interplay between hopping strength, stacking order and magnetic ground state. Here, utilizing angle-resolved photoelectron spectroscopy, we demonstrate the existence of magnetic nodal lines near Fermi level in an A-A stacking Kagome metal GdMn₆Sn₆, via imaging the conical in-plane dispersion at Brillouin zone boundary and strong out-of-plane dispersion, associated with the interlayer coupling of kagome sheets. More importantly, we directly observe the spin-orbit coupling effect in the out-of-plane ferrimagnetic phase of Tb doped GdMn₆Sn₆, which is absent in the undoped compound with in-plane magnetic order.  Our results not only provide the evidence of three-dimensional topological magnetic nodal lines in GdMn₆Sn₆ , but also experimentally illustrate the magnetic direction as the efficient tuning knob of the topological band structure in kagome materials.