Intrinsic optical absorption in Dirac metals

A Dirac metal is a doped (gated) material with the Fermi energy (EF) lying either in conduction or valence bands. In non-interacting picture, optical absorption gapless metals occurs only if frequency of incident photons (Ω) exceeds direct (Pauli) threshold, equal to 2EF. this work, we study, both analytically and numerically, role electron–electron (ee) electron–hole (eh) interactions two-dimensional (2D) three-dimensional (3D) entire interval frequencies below We show that, for Ω≪EF, conductivity, ℜσ(Ω), arising from combination ee certain eh scattering processes, scales as Ω2lnΩ 2D Ω2 3D, respectively, short-range (Hubbard) long-range (screened Coulomb) interactions. Another type similar Auger–Meitner (AM) processes atomic physics, starts contribute Ω above EF. Similar case semiconductors parabolic bands studied prior literature, AM contribution ℜσ(Ω) manifested by threshold singularity, ℜσ(Ω)∝(Ω−EF)d+2, where d spatial dimensionality 0<Ω−EF≪EF. contrast semiconductors, however, completely overshadowed other contributions. Numerically, happens be small almost range Ω<2EF. This finding may have important consequences collective modes