Time-reversal symmetry breaking type-II Weyl state in YbMnBi2

Abstract

Spectroscopic detection of Dirac and Weyl fermions in real materials is vital for both, promising applications and fundamental bridge between high-energy and condensed-matter physics. While the presence of Dirac and noncentrosymmetric Weyl fermions is well established in many materials, the magnetic Weyl semimetals still escape direct experimental detection. In order to find a time-reversal symmetry breaking Weyl state we design two materials and present here experimental and theoretical evidence of realization of such a state in one of them, YbMnBi 2 . We model the time-reversal symmetry breaking observed by magnetization and magneto-optical microscopy measurements by canted antiferromagnetism and find a number of Weyl points. Using angle-resolved photoemission, we directly observe two pairs of Weyl points connected by the Fermi arcs. Our results not only provide a fundamental link between the two areas of physics, but also demonstrate the practical way to design novel materials with exotic properties.

Magnetic structure and excitations of the topological semimetal YbMnBi2

“…Below T N , the magnetic susceptibility becomes strongly anisotropic with respect to applied field, where χ a > χ c . This bifurcation of χ(T ) at T N suggests that the manganese moments, in the ordered phase, are more susceptible to an in-plane field than a field applied along the c-axis, in agreement with earlier reports 10,14 . At low temperatures (below 50 K), the susceptibility grows in both field directions.…”

“…We have not ruled out the possibility of spin canting at the surface, which could reconcile the present results with those of Ref. 10. The lack of any anomalous features in the magnon spectrum implies a weak coupling between magnetism and the topological charge carriers.…”

“…In Ref. 10, it was argued that creation of Weyl points by TRS breaking in YbMnBi 2 requires a ∼10 • canting of the Mn moments away from the c-axis. If present, this canting would generate a net ferromagnetic component in the ab-plane of YbMnBi 2 , and would account for the Weyl nodes and arcs observed in the ARPES data.…”

Topological Semimetals in Square-Net Materials

“…In recent times, the square net has been linked to a very different kind of material property. Many intermetallic compounds that are isostructural or structurally related to iron-based superconductors have been shown to be topological semimetals (TSMs) (7,8,9,10,11,12,13,14,15,16,17).…”

Quantum transport in topological semimetals under magnetic fields (II)

“…Their energy bands touch at the Weyl nodes which host monopoles. The Weyl nodes have been verified in the Dirac semimetals Na 3 Bi [24,29,30] and Cd 3 As 2 [4,26,[31][32][33][34][35][36], and the Weyl semimetal TaAs family [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52], TaIrTe 4 [53] and YbMnBi 2 [54]. Also, Weyl semimetals can be induced from half-Heusler compounds by applying magnetic fields [55][56][57].…”