Exotic phenomena in topological Weyl line magnets

Topological electronic phases in intrinsic magnets are of current interest. One common magnetic topological object is the Weyl line, a two-fold band degeneracy along a closed curve in bulk momentum space. Weyl lines arise naturally in the absence of time-reversal symmetry (absent in magnets) and in the presence of mirror symmetry (common in many space groups). I will present the observation of Weyl lines by ARPES in the room temperature magnet Co₂MnGa [1]. On the surface of the magnet, I observe drumhead surface states, pinpointing the bulk-boundary correspondence and suggesting a Berry phase topological invariant associated with the Weyl line. Next, the intrinsic Berry curvature contribution to the anomalous Hall response, determined from quantum transport, agrees with a prediction of the Weyl line Berry curvature based on ARPES and first-principles calculations [1]. I will comment on composite topological structures arising from pinning and linking of different Weyl lines. Lastly, I will discuss future directions in Co₂MnGa and other topological Weyl line magnets.

[1] I. Belopolski*, K. Manna*, D. S. Sanchez*, G. Chang* et al. Science 365, 1278 (2019).