Figure 66.

(a) Red arrows indicate in-plane spin directions at zero field. Black arrows indicate the moment direction in a c-axis aligned field. (b) Spin-wave branches for one acoustic and two optical bands. The middle and top green arrows indicate Dirac points and band top, respectively. (c) Nearest-neighbor DMI direction. (d) DMI induced spin gap at Dirac points. (e) Neutron scattering measured spin waves energy/moment map at (a) 0 T, (b) 2 T, (c) 7 T; (d) Calculated neutron spectra for 7 T. All panels are adapted with permission from ref (767). Copyright 2015 American Physical Society.