Tetrahedral triple-Q ordering in the metallic triangular lattice antiferromagnet Co1/3TaS2

The triangular lattice antiferromagnet (TLAF) has been the standard paradigm of frustrated magnetism for several decades. The most common magnetic ordering in insulating TLAFs is the 120 structure. However, a fundamentally new triple-Q chiral state can emerge in metallic TLAFs, which represents the short wavelength limit of magnetic skyrmion crystals. We report the metallic TLAF Co1/3TaS2 as the first example of tetrahedral triple-Q ordering with the associated topological Hall effect (non-zero {\sigma}xy(H=0)) and uniform orbital magnetization Mz(H=0). Our measurements of the inelastic neutron scattering cross section are also consistent with the calculated dynamical structure factor of the tetrahedral triple-Q state.