Abstract

In noncollinear magnets (NCM), the winding spin texture defines a topological charge density and, related, an emergent electromagnetic field (EEMF) that bends the path of conduction electrons. Non-dissipative or low-energy ‘green’ computing is thought to be feasible by exploiting this EEMF. Despite recent progress in large-scale computing, full ab-initio calculation of the EEMF for real materials has remained a challenge for two decades. The Co(Nb/Ta)3S6 family realizes antiferromagnetism with a canted four-sublattice texture, which represents an atomistic analogon (< 2 nm size) to larger skyrmion spin vortices (~20-200 nm) [1,2]. Here, full ab-initio theory is consistent with the observed Hall and giant Nernst responses and shows two driving principles for large emergent electromagnetic fields in Co(Nb/Ta)3S6: First, a topological nodal plane in the parent, paramagnetic state, which is gapped by the four-sublattice order. And second, a spin-space group symmetry in the ordered state that realizes a non-Kramers band near-degeneracy over the full Brillouin zone. We also briefly touch on ab-initio calculations for the topological pyrochlore oxide Nd2Mo2O7 [4].

[1] P. Park et al., Nat. Commun. 14, 8346 (2023)
[2] H. Takagi et al., Nat. Phys. 19, 961 (2023)
[3] N.D. Khanh, M. Hirschberger, et al., under review (2024)
[4] M. Hirschberger et al., Phys. Rev. B 103, L041111 (2021)