Richard L. Greene Dissertation Award in Experimental Condensed Matter or Materials Physics: Discovery of magnetic Weyl semimetals and topological chiral crystals

The discovery of novel, robust topological materials is essential for advancing the state-of-the-art in topological physics. In this talk, I will discuss two fundamental strategies, using intrinsic magnetic order and structural crystalline chirality, which we have recently developed to uncover exotic quantum materials dominated by robust topological electronic states. I will first present the experimental observation of Weyl fermion loops and topological drumhead surface states by ARPES in the room-temperature ferromagnet Co₂MnGa [1]. Then, I will provide evidence that Co₂MnGa at the Fermi level is dominated by Berry curvature concentrated by the Weyl loops, driving a giant anomalous Hall effect and record-high anomalous Nernst effect, up to room temperature. Next, I will present our discovery by ARPES of the near-ideal topological chiral crystals RhSi and CoSi [2]. After reviewing our rigorous criteria for the experimental detection of topological Fermi arcs by ARPES [3,4], I will present our observation in these materials of giant helicoid Fermi arc surface states, arising from bulk topological chiral fermions with maximal momentum-space separation. Time permitting, I will comment on a third fundamental strategy, topological multilayers, which offers new opportunities for the future discovery of highly-tunable topological magnets [5].

[1] Ilya Belopolski et al. Science 365, 1278 (2019)
[2] Daniel Sanchez*, Ilya Belopolski* et al. Nature 567, 500 (2019)
[3] Su-Yang Xu*, Ilya Belopolski* et al. Science 349, 613 (2015)
[4] Ilya Belopolski et al. Phys. Rev. Lett. 116, 066802 (2016)
[5] Ilya Belopolski et al. Sci. Adv. 3, e1501692 (2017)