Quantum oscillations of optical absorption in Nb/Cu multilayer structures:Relation to the topology of the Fermi surface

For multilayer Nb/Cu films produced by high-frequency sputtering onto Si(10 0) substrates, the dispersion of effective indices of refraction n(eff) and absorption k(eff) was investigated by the ellipsometrical method in a spec tral range of lambda = 0.25-10 mu m. The reflectivity, real (epsilon'(eff)) and imaginary (epsilon "(eff)) parts of the dielectric permittivity, optic al conductivity sigma(eff), as well as the plasma (Omega(eff)) and relaxati on (gamma(eff)) frequencies of conduction electrons were: found to oscillat e depending on the niobium layer thickness. It was shown that the oscillati on period of the optical and electronic characteristics Delta L = 5 Angstro m can be related to the dimensions of the main sheets of the Fermi surface for niobium. The distinction in the thickness dependence of the optical pro perties of Nb/Cu multilayers in the regions of the intraband and interband mechanisms of light absorption is discussed.