Fermi surface of CrNb₃S₆: giant spin-orbit effect

Chiral magnets are of particular interest because of their exotic magnetic and transport properties. In the case of CrNb₃S₆, the ground-state magnetic configuration is a planar flat spiral with a periodicity of 48nm along the hexagonal c axis. Moderate external fields (H) alter the spin texture into the chiral soliton lattice (H⊥c) or the chiral conical phase (H ∥c). With increasing H, these phases continuously transform into forced ferromagnetic (FM) configurations that appear at H ~ 0.2 (⊥c) and 2 Tesla (∥c). Using a density functional theory approach, we investigate the FM state of CrNb₃S₆, paying particular attention to the spin-orbit coupling (SOC) and its effect on the electronic band structure and Fermi surface. Importantly, for some bands near the Fermi level, SOC introduces giant and peculiar first-order changes of the band energies when the magnetization is parallel to the c axis: the band dispersion appears to be shifted in k space. Consequently, the deformed Fermi surface has a highly asymmetric shape that could lead to nonreciprocal transport. Symmetry arguments and detailed analysis of SOC effects will be given.