Mid-infrared radiative properties of high-Tc superconductive Y-Ba-Cu-O thin films at low temperatures - I: experiments

摘要

The transmittance and reflectance of superconductive y Ba-Cu-O (YBCO) thin films deposited on MgO substrates have been measured in the mid-infrared wavelength region from 2.5 to 25μm (wavenumber from 400 to 4000cm{sup}(-1)) and at temperatures between 20 and 300K by using a Bio-Rad FT-IR spectrometer. Three measured YBa{sub}2Cu{sub}3O{sub}7 thin films are c-axis oriented with three different thicknesses 23, 55, and 113nm. The results show that the transmittance of Y-Ba-Cu-O films is influenced insignificantly with decreasing temperature. As the temperature decreases, the substrate reflectance increases at longer wavelengths, while it varies slightly at shorter wavelengths. Furthermore, the results also indicate that a decrease in the film thickness often leads to an increase in the film/substrate absorptance for both the normal and superconducting states in the mid-infrared region, and this can be used to explain the increase of the responsivity of high-T{sub}c superconducthig infrared detectors achieved by using thinner films.