Flux flow instability as a probe for quasiparticle energy relaxation time in Fe-chalcogenides

In this work, we aim to demonstrate the potential of the flux flow instability (FFI) tool as a probe for the evaluation of the quasiparticle energy relaxation time τ in iron-based superconductors (IBS). The knowledge of this microscopic parameter, its temperature dependence and the magnetic field influence, turns particularly useful to implement IBS materials in photon detection applications, as well as to get information on the gap symmetry or its anisotropy. Here, we focus on Fe(Se,Te) thin films that both from structural and magnetic properties show the simpler behaviour, thus it can be a reference test for any more complex IBS. By current-voltage characterizations and resistance measurements, we investigate the FFI features in the presence of an external applied magnetic field as a function of the angular dependence between the crystal structure of the film and the orientation of the field. We describe the observed experimental characteristics of FFI within the intrinsic electronic mechanism of Larkin-Ovchinnikov model. In this way, we are able to give a quantitative estimate of τ in Fe(Se,Te) that can be compared with evaluation from other techniques such as pump and probe measurements. Thus, the angular measurements of FFI in high magnetic fields are a viable route to the possible mechanisms of quasiparticle relaxation and to the complementary knowledge on its anisotropy.