SPECTROSCOPIC ELLIPSOMETRY ON 1T-TISE2

Ellipsometric measurements of the quasi-two-dimensional layered compound TiSe2, over the spectral range 1 eV < HBARomega < 24 eV reveal a variety of structures owing to interband transitions. By analysing the spectral dependence of the real and imaginary parts of the dielectric function both the energies of the critical points and their type have been determined assuming an isotropic model. To verify the applicability of this approach the quotient of the reflectivity for parallel and perpendicular polarizations was measured for angles of incidence between 30-degrees and 80-degrees and compared with the values calculated from the ellipsometric data. Rather surprisingly we find that the ellipsometric measurements mirror the dielectric function of the ordinary ray with the electric field vector perpendicular to the c axis. This result can be understood qualitatively in terms of the magnitude of the refractive index which effectively reduces the optical anisotropy.