Complex conductivity of the FeSe_1-<i>x</i>Te<i>_x</i> films

We measured the complex conductivity, σ, of the FeSe_1-xTe_x films below T_c which show a drastic increase of the superconducting transition temperature, T_c, when the nematic order disappears. Since the magnetic penetration depth, λ(> 400 nm) of Fe(Se,Te) is longer than the typical thickness of the film (~100 nm), we combined the coplanar-waveguide-resonator- and cavity-perturbation techniques to evaluate both the real and imaginary part of σ. The film with the nematic order showed a qualitatively different behavior in the quasiparticle scattering time compared with those without the nematic order, suggesting that the nematic order strongly influences the superconducting gap structure. On the other hand, T_c was proportional to n_s/m* (∝λ^-2) irrespective with the presence or the absence of the nematic order. This result indicates that the amount of the superfluid has a stronger impact on T_c of Fe(Se,Te) than the nematic order itself.