Terahertz properties and the negative dielectric regions in boron nitride

Terahertz anomalous dispersion and material physical properties leads to form the region with negative dielectric permittivity (DP) that is created around the polar frequency oscillations in three crystalline modifications of boron nitride will be analyzed in our report. Our analysis based on the simple quantitative criterion of existence the negative DP bands. Seven vibrations in different crystalline modifications of boron nitride have been studied and it is shown the applicability of our criterion to crystals analysis with a complex set of polar phonons.