Measuring Complex Refractive Indices of a Nanometer-Thick Superconducting Film Using Terahertz Time-Domain Spectroscopy with a 10 Femtoseconds Pulse Laser

Superconducting thin films are widely applied in various fields, including switching devices, because of their phase transition behaviors relation to temperature changes. Therefore, it is important quantitatively determine the optical constant a superconducting material thin-film state. We performed terahertz time-domain spectroscopy, based on 10 femtoseconds pulse laser, measure GdBa2Cu3O7?x (GdBCO) film region. then estimated refractive indices 70 nm-thick GdBCO using numerical extraction process, even though thickness was approximately 1/10,000 times smaller than wavelength range 200 ?m 1 mm. The resulting were consistent with theoretical results two-fluid model. Our work will help further understand properties thicknesses under 100 nm, as well provide standard platform for characterizing without need Kramers–Kronig transformation at frequencies.