PC8-6

Complex conductivity of FeSe1-xTex­ (x=0.1-0.5) film

Dec.3 14:45-15:00 (Tokyo Time)

*Hodaka Kurokawa1, Sota Nakamura1, Jiahui Zhao1, Naoki Shikama1, Yuki Sakishita1, Yue Sun2, Fuyuki Nabeshima1, Yoshinori Imai3, Haruhisa Kitano2, Atsutaka Maeda1

The University of Tokyo, Japan1

Aoyama Gakuin University, Japan2

Tohoku University, Japan3

The iron chalcogenide superconductor, Fe(Se,Te), has been attracting broad interests because of its potential ability for high-Tc superconductivity, the absence of the magnetic order under the ambient pressure, and the topological nature. In the Fe(Se,Te) film, it has been revealed that the superconducting transition temperature, Tc, increases almost twice when the nematic order disappears with increasing Te content [1]. In addition, the close correlation between the carrier density in the normal state and the Tc was observed in the Fe(Se,Te) and Fe(Se,S) film irrespective with the nematic order, indicating that the existence of the nematic order has less dominant contribution to the Tc than the carrier density [2]. However, it is still unclear whether the same trend exists in the superfluid density or not. Hence, in order to clarify the impact of the Te substitution on the electronic structure of Fe(Se,Te) and its relation to Tc, we measured the complex conductivity of FeSe1-xTex­ (x=0.1-0.5) film in the superconducting state.

The real part of the complex conductivity, σ1, was measured using the cavity perturbation technique. The quasiparticle scattering time, τ, was calculated from σ1. Comparing the temperature dependence of τ among different compositions, no significant systematic changes were observed with increasing Te content in the temperature range, 0.2 Tc-0.75 Tc. On the other hand, the imaginary part of the complex conductivity, σ2∝λ-2, measured by the superconducting coplanar resonator fabricated from the Fe(Se,Te) film, was found to correlate with Tc, and the so-called “Uemura relation” was observed. This indicates that the superfluid density, ns∝λ-2, plays a crucial role in the determination of Tc. The trend is consistent with the correlation found between Tc and the carrier density in the normal state. These results suggest that although the nematic order can change the electronic structure of the iron chalcogenide superconductors, the amount of the (superfluid) carrier density has the most direct correlation with Tc.

【References】
[1] Y. Imai et al., PNAS 112, 1937 (2015).
[2] F. Nabeshima et al., PRB 101, 184517 (2020).

Keywords: iron chalcogenide superconductor, microwave, complex conductivity, penetration depth