Optical Determination of Dielectric Constant in Black Phosphorus

Three components of dielectric constant along three principal crystal axes in black phosphorus are determined for the first time. Two of them are obtained from far-infrared interference spectra for thin cleaved samples. The remaining one is determined by analyzing far-infrared absorption peaks observed in p-type sample at 1.4 K, which are ascribed to optical transitions from the acceptor ground state to its excited states.