Optical absorption in two-dimensional materials with tilted Dirac cones

The interband optical absorption of linearly polarized light by two-dimensional (2D) semimetals hosting tilted and anisotropic Dirac cones in the band structure is analysed theoretically. Supercritically (type-II) are characterized an that highly dependent on incident photon polarization frequency tunable changing Fermi level with a back-gate voltage. Type-II exhibit open surfaces large regions Brillouin zone where valence conduction bands sit either above or below level. As consequence, unlike their subcritically (type-I) counterparts, type-II have many states Pauli blocked even when tuned to crossing point. We analyze interplay tilt parameter velocity anisotropy, demonstrating response cone cannot be described its alone. special case our general theory, we discuss proposed 2D type-I semimetal 8-$Pmmn$ borophene. Guided in-depth analytics, develop recipe fully characterize anisotropy any solely from spectrum. expect paper encourage engineering as major route create gate-tunable thin-film polarizers.