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TT: Fachverband Tiefe Temperaturen

TT 16: Superconductivity: Properties and Electronic Structure II

TT 16.6: Talk

Tuesday, March 18, 2025, 10:45–11:00, H32

Two-fluid model analysis of the terahertz conductivity of YBaCuO samples: Optimally doped, underdoped and overdoped cases — •Christelle Kadlec¹, Wen-Yen Tzeng², Chih-Wei Luo³, Jiunn-Yuan Lin³, and Michal Šindler¹ — ¹Institute of Physics, Prague, Czech Republic — ²National Formosa University, Yunlin, Taiwan — ³National Yang Ming Chiao Tung University, Hsinchu, Taiwan

The conductivity of a high-quality overdoped Y_0.7Ca_0.3Ba₂Cu₃O_7−δ film and of underdoped and optimally doped films of its parent compound YBa₂Cu₃O_7−δ was measured using time-domain terahertz spectroscopy. In the normal state, the frequency dependence of the complex conductivity is described by the Drude model. Below the critical temperature T_c, the two-fluid model was successfully employed to fit all the spectra, from 5 K up to T_c. The temperature behaviour of fundamental parameters such as the scattering rate 1/τ, the superfluid (normal) fraction f_s (f_n) and the complex conductivity σ was investigated at given frequencies. We observed that a fifth of the electrons do not condense to the superfluid fraction even at 5 K for the optimally doped and overdoped samples. The real part of the conductivity σ₁(T) exhibits a peak for low frequencies. It can be observed for all three compounds and its exact shape depends on the quality of the sample. A further analysis shows that this peak is a consequence of the competition between the scattering time τ(T) and the superfluid fraction f_s(T).

For further details, see https://arxiv.org/pdf/2309.17408

Keywords: High temperature superconductors; YBaCuO or YBCO; THz spectroscopy; Two-fluid model; YCaBaCuO