Spin-Canting-Induced Band Reconstruction in the Dirac Material Ca1−xNaxMnBi2

The ternary AMnBi2 (A is alkaline as well as rare-earth atom) materials provide an arena for investigating the interplay between low-dimensional magnetism of the antiferromagnetic MnBi layers and the electronic states in the intercalated Bi layers, which harbor relativistic fermions. Here, we report on a comprehensive study of the optical properties and magnetic torque response of Ca1−xNaxMnBi2. Our findings give evidence for a spin canting occurring at Ts∼50–100 K. With the support of first-principles calculations we establish a direct link between the spin canting and the reconstruction of the electronic band structure, having immediate implications for the spectral weight reshuffling in the optical response, signaling a partial gapping of the Fermi surface, and the dc transport properties below Ts.