Friday, 10 January 2014

Terahertz electrodynamics and superconducting energy gap of NbTiN

Taeyoon Hong1Kyujin Choi1Kyung Ik Sim1Taewoo Ha1Byung Cheol Park1,Hirotake Yamamori2 and Jae Hoon Kim1,a)


Terahertz electrodynamics of superconducting NbTiN has been studied in the spectral range of 8-70 cm–1 above and below the critical temperature of  = 14.1 K. Our transmission terahertz time-domain spectroscopy technique allows for independent and accurate determination of both the real part σ and the imaginary part σ of the optical conductivity σ as a function of frequency ω and temperature  without a Kramers-Kronig analysis. A clear signature of the superconducting energy gap Δ() is observed in the real part σ of the optical conductivity below, with 2Δ(0) = 36.5 cm−1 corresponding to 2Δ(0)/ = 3.72. No indication of strong-coupling effects was observed in the imaginary part σ toward zero frequency. Our results, including the temperature dependence of the penetration depth λ(), are in excellent quantitative agreement with weak coupling BCS theory and Mattis-Bardeen formula.

This study was performed using TeraView's TPS Spectra 3000 system. (TeraView, Cambridge, UK)