Terahertz electrodynamics and superconducting energy gap of NbTiN

Taeyoon Hong¹, Kyujin Choi¹, Kyung Ik Sim¹, Taewoo Ha¹, Byung Cheol Park¹,Hirotake Yamamori² and Jae Hoon Kim^1,a)

Abstract

Terahertz electrodynamics of superconducting NbTiN has been studied in the spectral range of 8-70 cm^–1 above and below the critical temperature of Tc  = 14.1 K. Our transmission terahertz time-domain spectroscopy technique allows for independent and accurate determination of both the real part σ1 and the imaginary part σ2 of the optical conductivity σ as a function of frequency ω and temperature T without a Kramers-Kronig analysis. A clear signature of the superconducting energy gap Δ(T) is observed in the real part σ1 of the optical conductivity belowTc , with 2Δ(0) = 36.5 cm⁻¹ corresponding to 2Δ(0)/kBTc  = 3.72. No indication of strong-coupling effects was observed in the imaginary part σ2 toward zero frequency. Our results, including the temperature dependence of the penetration depth λ(T), 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)

Full Article: http://scitation.aip.org/content/aip/journal/jap/114/24/10.1063/1.4856995