FAR-INFRARED REFLECTANCE AND TRANSMITTANCE STUDIES OF YBa2Cu3O7-x SINGLE-CRYSTAL THIN FILMS

• Published in: Jpn.J.Appl.Phys ,Part 1. Vol. 40, no. 5A, pp. 3163-3170. 2001 Vol. 40; no. 5A; pp. 3163 - 3170
• Main Authors: Shibata, H, Kimura, S, Kashiwaya, S, Ueno, S, Koyanagi, M, Terada, N
• Format: Journal Article
• Language: English
• Published: 2001
• ISSN: 0021-4922
• DOI: 10.1143/JJAP.40.3163

A new method of estimating the optical constants of thin films has been developed and applied to YBa2Cu3O7-x epitaxial single-crystal thin films (Tc=90 K) grown on MgO substrates to determine the far-ir optical conductivity sab(w), which is the response when an unpolarized excitation is applied parallel to the ab-plane in multidomain (twinned) single crystals of YBa2Cu3O7-x. In this method, both the transmittance spectra T(w) and reflectance spectra R(w) are measured as a function of the wave number w, and the results are substituted into a set of coupled equations which exactly describe R(w) and T(w) of thin films on substrates, where the complex refractive index N=n+ik of the thin films is an unknown parameter. The coupled equations are numerically solved using the Newton method, and the values of n and k are determined as a function of w. Authors have determined sab(w) of YBa2Cu3O7-x thin films for w=50-250 cm-1 at T=34-97 K. Analysis of the temperature dependence of sab(w) based on the two-fluid model suggests that the symmetry of the superconducting pairing state of the specimen is d-wave. 37 refs.