Photon absorption of two-dimensional non-symmorphic Dirac semimetals*

Graphene-like 2D Dirac materials are gapless only within certain approximations, e.g., if spin-orbit coupling (SOC) is neglected. It has recently been reported that materials with non-symmorphic crystal lattice possess symmetry-enforced Dirac-like band dispersion around certain high-symmetry momenta even in presence of SOC [1]. Here we calculate the optical absorption coefficient of non-symmorphic semimetals, such as α-bismuthene, which host two anisotropic Dirac cones with different Fermi velocities along x and y directions. We find that the optical absorption coefficient depends strongly on the anisotropy factor and the photon polarization. When a magnetic field is applied perpendicular to the plane the material, the absorption coefficient also depends on an internal parameter we termed the “mixing angle” of the band structure. Due to the anisotropy present in our model, the two Dirac cones contribute differently to the optical absorbance. Consequently, it is possible to selectively address one or the other cone and to control the magnitude of the optical absorbance by varying photon polarization .

[1] P.J. Kowalczyk et al., ACS Nano 14, 1888−1894 (2020).