Clean to dirty limit andT_csuppression in NdFeAsO_0.7F_0.3studied byH_c2analysis

Abstract

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 5.25×10 16 /cm 2 total -particle dose. For H||ab-plane, dHc2/dT does not vary remarkably with irradiation, while for H//c-axis it increases sharply after the first irradiation of 3.60×10 15 /cm 2 and then more gradually with further irradiation doses. Focusing on H||c-axis, we develop a phenomenological analysis of the Hc2 slope which allows 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 BCS to the mean free path  and we find that when the Tc is reduced by a factor of 4 from its pristine value, BCS/ becomes as large as 7 and  reaches values ~1.8 nm, indicating that NdFeAs(O,F) is well into the dirty regime. Our analysis of the Hc2 slope also allows to compare the pair-breaking effectiveness of scattering in different superconductors, showing that it is comparable in NdFeAs(O,F) and in moderatetemperature phonon-mediated superconductors such as MgB2 and A15 compounds, but much stronger in YBa2Cu3O7-. This work thus shows that dHc2/dT is a figure of merit, alternative to the residual resistivity, to investigate the pair-breaking mechanism induced by impurity scattering in superconductors.

Roles of electron mean free path and flux pinning in optimizing the critical current in YBCO superconductors

“…The main panel of figure 3(b) shows the measured T c values as the function of ℓ and the fit to equation (11). The obtained fitting parameter is α = 0.042, which is of the same order of magnitude as observed earlier [43]. It is clear from figure 3(b) that the maximum value of T c in the data is close to 87 K instead of the generally agreed 92 K for YBCO.…”

“…In the traditional view, the critical temperature, T c , should not be affected by non-magnetic impurities [41,42], but they do lower the T c in HTS [43,44]. It has been modelled with the Abrikosov-Gor'kov theory, which can be written as [43]…”

The role of texturing and thickness of oxide buffer layers in the superconducting properties of Fe(Se,Te) Coated Conductors

“…Here is therefore compared, the average value of ∆H c2 /∆T between 0 and 4 T, which goes from about 6 T K −1 on the thick ceria to as high as 21 T K −1 for the film on Hastelloy. These different values for the two samples can be related to the higher level of disorder of the latter sample, and thus to its much smaller mean free path [40]. On the other hand, the irreversibility fields of the two samples are very different in shape, as H irr of the film on thick native oxide of Hastelloy presents a pronounced upward curvature and it is much smaller in value.…”

Влияние Внутригранульных Мейсснеровских Токов И Захваченного В Гранулах Потока На Эффективное Поле В Межгранульной Среде И Гистерезис Магнитосопротивления Гранулярного ВТСП

“…Исследования магнитотранспортных свойств получаемых сверхпроводящих материалов являются неотъемлемой частью их характеризации [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Это касается как, ставших уже " классическими", гранулярных высокотемпературных сверхпроводников (ВТСП), так и новых, " гидридных" сверхпроводников [13,14].…”