Birefringence of Cu2ZnSiSe4 single crystals

In Cu2ZnSiSe4 single crystals an interference spectra of the Fabry-Perot type due to observed birefringence were studied and spectral dependence of the refractive index n|| (E || c) and n⊥ (E ⊥ c), which intersect at isotropic wavelength λ0 = 622 nm (300 K) and 605 nm (10 K) were defined. The spectral dependence of Δn = n⊥-n|| in the short-wave and long-wave side of the wavelength λ0 was determined. It was found that when λ > λ0 Δn is negative and when λ < λ0 Δn is positive. Wavelength λ0 shifts as the temperature decreases toward shorter wavelengths. Phases of the n|| and n⊥ light waves in λ > λ0 and λ < λ0 are different. At a wavelength of 538 nm (10 K) Δn has a maximum. Absorption coefficient in the fringes varies up to 102-103 times.