Parity-broken chiral spin dynamics in Ba₃NbFe₃Si₂O₁₄.

The spin-wave excitations emerging from the chiral helically modulated 120° magnetic order in a langasite Ba₃NbFe₃Si₂O₁₄ enantiopure crystal were investigated by unpolarized and polarized inelastic neutron scattering. A dynamical fingerprint of the chiral ground state is obtained, singularized by (i) spectral weight asymmetries answerable to the structural chirality and (ii) a full chirality of the spin correlations observed over the whole energy spectrum. The intrinsic chiral nature of the spin waves' elementary excitations is shown in the absence of macroscopic time-reversal symmetry breaking.