Optical Properties of Superconducting NbTi Thin Films in the Terahertz Region

We conducted a comprehensive spectroscopic examination of superconducting NbTi thin films using terahertz time-domain spectroscopy in the spectral range from 10 to 70 cm^-1 and a temperature range from 1.5 K to 8.5 K. Additionally, we applied external in-plane magnetic fields up to 7 T. We obtained the transmission coefficient, which enabled the determination of the optical conductivity of the NbTi thin films. We confirmed the critical temperature of 8 K and acquired the temperature dependence of the superconducting gap. Moreover, our analysis revealed a remarkable feature in the superconducting NbTi thin films under the influence of in-plane magnetic fields, particularly related to pair breaking. Our research provides valuable insights into the behaviour of NbTi thin films under varying temperatures and in-plane magnetic fields in the terahertz frequency range.