Unusual microwave response and bulk conductivity of very thin fese0.3te0.7 films as a function of temperature

TL;DR

This study investigates the microwave response and bulk conductivity of very thin FeSe0.3Te0.7 films, revealing unique temperature-dependent behaviors and supporting a two-gap s(+-)-wave superconductivity model.

Contribution

It provides new insights into the microwave properties of thin FeSeTe films and supports a two-gap s(+-)-wave pairing symmetry through experimental fitting.

Findings

Peak in surface resistance near Tc

Power-law behavior of magnetic penetration depth with n=2.4

Two-gap model fitting supports s(+-)-wave symmetry

Abstract

Results of X-band microwave surface impedance measurements of FeSe1-xTex very thin film are reported. The effective surface resistance shows appearance of peak at T less and near Tc when plotted as function of temperature. The authors suggests that the most well-reasoned explanation can be based on the idea of the changing orientation of the microwave magnetic field at a SN phase transition near the surface of a very thin film. The magnetic penetration depth exhibits a power-law behavior of delta lambda proportional to T with an exponent n = 2.4 at low temperatures, which is noticeably higher than in the published results on FeSe1-xTexsingle crystal. However the temperature dependence of the superfluid conductivity remains very different from the behavior described by the BCS theory. Experimental results are fitted very well by a two-gap model with delta1/kTc=0.43 and delta2/kTc=1.22,thus supporting s(+-)- wave symmetry. The rapid increase of the quasiparticle scattering time is obtained from the microwave impedance measurements.