Optical Properties of Graphite in the Far-Infrared Region

The transverse dielectric function ε = ε 1 + i ε 2 of graphite for the electromagnetic wave normally incident on the trigonal plane is calculated on the basis of the band structure for the far-infrared region where the effects of free carriers and the spin orbit coupling are predominant. In the absorption spectrum there appears van Hove singularity arising from the transition between the two degenerate bands near point K of the Brillouin zone split by the effect of spin orbit coupling, but no observable structures from the vicinity of point H . The plasma due to free carriers is markedly affected by the interband effect. The strength of spin orbit coupling λ 33 z is not determined definitely from the experiment available, but is estimated as 0.004eV (at point H ) or 0.0055eV (at point K ) as one of possible values.