NMR observation of extreme type-II superconductivity in A method of estimating penetration depth

We present a method of estimating the penetration depth (Formula presented) for extreme type-II superconductors that exhibit powder-pattern NMR line shapes in which the anisotropy of the shifts dominates the effect of magnetic field distribution. In this method, we regard the increase in the broadening, not that in the width of the overall line shape, as the field distribution defined in the Pincus’s formula [Pincus et al., Phys. Lett. 13, 21 (1964)]. Applying this method to the previous result of (Formula presented) NMR line shapes for (Formula presented) we found that (Formula presented) 8100 Å, which is consistent with the value of 8900 Å recently obtained from precise low-field magnetization measurements [Buntar et al., Phys. Rev. B 54, R9651 (1996)]. This validates not only the present method but also the data and analyses of the (Formula presented) NMR line shapes so far. We also discuss why values of (Formula presented) smaller than the real one were reported in the early stage of the study of (Formula presented) superconductivity.