Penetration depth, multiband superconductivity, and absence of   muon-induced perturbation in superconducting PrOs$_{4}$Sb$_{12}$
  Transverse-field muon spin rotation ($\mu$SR) experiments in the heavy-fermion superconductor PrOs$_{4}$Sb$_{12}$ ($T_{c}=1.85$ K) suggest that the superconducting penetration depth $\lambda(T)$ is temperature-independent at low temperatures, consistent with a gapped quasiparticle excitation spectrum. In contrast, radiofrequency (rf) inductive measurements yield a stronger temperature dependence of $\lambda(T)$, indicative of point nodes in the gap. This discrepancy appears to be related to the multiband structure of PrOs$_{4}$Sb$_{12}$. Muon Knight shift measurements in PrOs$_{4}$Sb$_{12}$ suggest that the perturbing effect of the muon charge on the neighboring Pr$^{3+}$ crystalline electric field is negligibly small, and therefore is unlikely to cause the difference between the $\mu$SR and rf results. 
Lei Shu, D. E. MacLaughlin, W. P. Beyermann, R. H. Heffner, G. D.   Morris, O. O. Bernal, F. D. Callaghan, J. E. Sonier, W. ...