Study the optical properties of Pr2CuO4 thin films with different Tc0 via spectroscopic ellipsometry

Abstract

In this work, we primarily present spectroscopic ellipsometry (SE) study on Pr2CuO4 (PCO) thin films, a parent compound of electron-doped cuprate superconductors. The c-aixs orientation films with various superconducting transition temperature Tc0 were prepared by a chemical method, which are single phase and good crystallinity verified by x-ray diffraction. The imaginary part of dielectric function (εi) of PCO was investigated by SE using a four-layer optical model in the photon energy range from 1.55 to 4.13 eV. Through fitting the second derivative spectra of εi via critical point model, we find that the charge-transfer gap exists in PCO system and, more importantly, this gap has a negative relationship with Tc0. This viewpoint demonstrates that the charge-transfer gap would merge together with the electrons doping in PCO and opens a door to understand the nature of cuprate superconductors.