In this work, we investigate the temperature dependence of the upper critical field, dHc2/dT, in an increasingly disordered NdFeAsO0.7F0.3 (NdFeAs(O,F)) single crystal that has been progressively irradiated up to a 5.25×1016 cm−2 total α-particle dose. For the H||ab-plane, dHc2/dT does not vary remarkably with irradiation, while for the H||c-axis it increases sharply after the first irradiation of 3.60×1015 cm−2 and then more gradually with further irradiation doses. Focusing on the H||caxis, we develop a phenomenological analysis of the Hc2 slope which allows us to inspect the crossover from the clean to the dirty regime. From the Hc2 slope normalized to the critical temperature and to its clean limit value, we extract the ratio of the coherence length ξBCS to the mean free path ℓ and we find that when Tc is reduced by a factor of four from its pristine value, ξBCS/ℓ becomes as large as ∼7 and ℓ reaches values of ∼1.8 nm, indicating that NdFeAs(O,F) is well into the dirty regime. Our analysis of the Hc2 slope also allows us to compare the pair-breaking effectiveness of scattering in different superconductors, showing similarity between unconventional NdFeAs(O,F) and moderate-Tc phonon-mediated devices, such as MgB2 and A15 compounds, but much a stronger difference with YBa2Cu3O7-δ. This work thus shows that dHc2/dT is a reliable parameter, providing an alternative to residual resistivity, for investigating the pair-breaking mechanism induced by impurity scattering in superconductors.
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|Titolo:||Clean to dirty limit and T c suppression in NdFeAsO0.7F0.3 studied by H c2 analysis|
|Data di pubblicazione:||2018|
|Appare nelle tipologie:||01.01 - Articolo su rivista|