Muon spin relaxation measurements have been performed to obtain penetration depth versus temperature for several high-temperature oxide superconductors. Comparison with theoretical results based on the Eliashberg equations indicates that at 1 kOe the (RE)Ba2Cu3O7 materials (data for RE=Gd, Er, and Eu) are in the very strong coupling, extremely dirty limit, while data at 5 kOe for Bi2CaSr2Cu2O8 and Tl2Ca2Ba2Cu3O10 follow the strong coupling, clean limit curve.
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Lichti et al. (1989) studied this question.