Abstract
In the following, NMR and NQR measurements in the superconducting state of underdoped and optimally-doped LaO1−xF x FeAs with x = 0.05, x = 0.075 and x = 0.1 will be shown and discussed within possible gap symmetries. The presentation of the data is focussed on dynamic properties. Spin-lattice relaxation rate data for x = 0.05, x = 0.075 and x = 0.1 will be shown and analysed in Section 7.1. Section 7.2 reports the special case of LaO0.9F0.1FeAs1−δ, an optimally-doped sample with additional impurities (arsenic vacancies), exhibiting slightly enhanced superconducting properties and an even sharper decrease of T-11 than optimally-doped LaO0.9F0.1FeAs.
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Notes
- 1.
Note that within the sample series grown in the IFW Dresden, the sample with a nominal fluorine doping of \( x = 0.04 \) is not superconducting, but displays a structural and a magnetic phase transition at \( {T_s} = 151{\rm{K}} \) and \( {T_N} = 120{\rm{K}} \), respectively [135]. The LaO0.96F0.04FeAs sample displayed in Fig. 7.1 was grown in Hosono’s group [168].
- 2.
The impurity strength is given by \( \sigma =\frac{{{(\pi N(0)v)}^{2}}}{1+{{(\pi N(0)v)}^{2}}} \) where N(0) is the density of states at the Fermienergy and v is the impurity potential [176].
- 3.
The impurity scattering rate is given by \( {\gamma _{{\rm{interband}}}} = 0.8{\Delta _0} \), where ∆0 is the superconducting energy gap at low temperature without impurity scattering [176]
- 4.
Please refer to Appendix A.3 for a discussion of the use of the stretching exponent λ.
- 5.
Since Eq. (7.2) contains 8 parameters, the robustness of the fit was checked by fixing different parameters to reasonable values during different fitting sessions. For instance at a first run w was fixed to 0.81 and at a second run T 1s was fixed to 220ms. T 1sc resulted to be the same within error bars for all different checks. During the first run, T 1s lay in between 100 and 450 ms and during the second check w varied between 0.65 and 0.81, which are realistic values.
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© 2012 Vieweg+Teubner Verlag | Springer Fachmedien Wiesbaden
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Hammerath, F. (2012). NMR and NQR on LaO1−xF x FeAs in the Superconducting State. In: Magnetism and Superconductivity in Iron-based Superconductors as Probed by Nuclear Magnetic Resonance. Vieweg+Teubner Verlag, Wiesbaden. https://doi.org/10.1007/978-3-8348-2423-3_7
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DOI: https://doi.org/10.1007/978-3-8348-2423-3_7
Publisher Name: Vieweg+Teubner Verlag, Wiesbaden
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Online ISBN: 978-3-8348-2423-3
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