Obtaining The Scattering Rate Of Different T-C0 Fese Thin Films Via Spectroscopic Ellipsometry

Due to the simplest crystalline structure among Fe-based superconductors, the FeSe system has attracted a lot of attention. In this work, FeSe thin films grown on the CaF2 substrate with T-c0 = 6 and 11 K (named FeSe_1 and FeSe_2, respectively) are fabricated by a pulsed laser deposition technique. X-ray diffraction exhibits a high-quality single crystal of the two FeSe samples, and the lattice constants are about 5.574 angstrom. Atomic force microscopy characterizes their surface topography and roughness, which shows stripes in their surfaces that is helpful to construct a roughness layer using the optical measurement spectroscopic ellipsometry (SE) technique. SE is a powerful tool to determine FeSe thin films' complex refractive index N = n + ik and plasma oscillation frequency omega(p). These important parameters are related to scattering rate tau(-1) for FeSe thin films. The results show that scattering rate tau(-1) of FeSe_2 is significantly lower than that of FeSe_1 in the whole frequency testing range at room temperature, which may be the reason that FeSe_2 owns higher T-c0 in low temperature than FeSe_1. Published by the AVS.