Comparison of different methods for analyzingμSR line shapes in the vortex state of type-II superconductors

Abstract

A detailed analysis of muon-spin rotation(μSR) spectra in the vortex state of type-II superconductors using different theoretical models ispresented. Analytical approximations of the London and Ginzburg–Landau (GL) models,as well as an exact solution of the GL model were used. The limits of the validity of thesemodels and the reliability for extracting parameters such as the magnetic penetration depthλ and the coherencelength ξ from theexperimental μSR spectra were investigated. The analysis of the simulatedμSR spectra showed that at high magnetic fields there is a strong correlation betweenλ and ξ obtained for any value of the Ginzburg–Landau parameterκ = λ/ξ. The smaller the applied magnetic field, the smaller the possibility of finding the correct value ofξ. A simultaneousdetermination of λ and ξ without any restrictions is very problematic, regardless of the model used to describe the vortex state.It was found that for extreme type-II superconductors and low magnetic fields, the fitted value ofλ is practicallyindependent of ξ. The second-moment method frequently used to analyzeμSR spectra by means of a multi-component Gaussian fit generally yields reliable values ofλ over the whole range of applied fields (Hc1 and Hc2 are the first and second critical fields, respectively). These results are also relevant for theinterpretation of small-angle neutron scattering experiments on the vortex state in type-IIsuperconductors.