Complex conductivity of FeSe_1–xTe_x(x = 0 – 0.5) films

Abstract

We measured the complex conductivity, σ, of the FeSe1−x Te x (x = 0 – 0.5) 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 parts of σ. Films with the nematic order showed a qualitatively different behavior of the quasiparticle scattering time compared with those without the nematic order, suggesting that the nematic order influences the superconducting gap structure. On the other hand, the proportionality between the superfluid density, n s/m* (∝ λ−2), and T c was observed irrespective of the presence or 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 presence or absence of the nematic order itself.

Chemical pressure effect of the electron-doped FeSe films with an electric double-layer-transistor structure

“…A Magnetotransport experiment revealed a correlation between T c and carrier density [46], suggesting that the band reconstruction in the nematic phase predominantly affects the superconductivity rather than the existence of the nematic order itself or the nematic fluctuation possibly developing near the quantum critical point. Indeed, our recent DFT calculation showed a drastic change in DOS at the Fermi level before and after the nematic transition [47]. In contrast to the undoped FeSe, the e-doped FeSe does not exhibit the nematic order, as was suggested by the resistance measurement.…”