Abstract
Femtosecond spectroscopy has been used to investigate the quasiparticle relaxation times in a nearly optimally doped chalcogenide superconducting FeSe0.5Te0.5 thin film. It is characterized by an enhancement of the critical temperature Tc = 19.1 K by strain. Experimental results indicate the existence of a temperature dependence of the quasiparticle recombination time τR in the superconducting state where an energy gap Δ(T) is present. A fitting procedure based on a BCS-like assumption for τR gives Δ0 = 4.1 ± 0.4 meV for the superconducting energy gap extrapolated at T = 0, which corresponds to 2Δ0/kBTc = 4.9 ± 0.5. Accordingly, an estimation of the characteristic phonon energy and the electron–phonon coupling constant λ is reported and discussed. The obtained value λ ≈ 0.6 is in good agreement with other similar determinations obtained by different techniques and numerical approaches. The small value of λ confirms that a phonon-mediated coupling cannot be the only mechanism leading to the formation of the superconducting state in FeSeTe films.
Published Version
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