Novel features in the flux-flow resistivity of the heavy fermion superconductor PrOs₄Sb₁₂

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We have investigated the electrical resistivity of the heavy fermion superconductor PrOs₄Sb₁₂ in the mixed state. We found unusual double minima in the flux-flow resistivity as a function of magnetic field below the upper critical field for the first time, indicating double peaks in the pinning force density (F P). Estimated F P at the peak exhibits apparent dependence on applied field direction; composed of two-fold and four-fold symmetries mimicking the reported angular dependence of thermal conductivity (κ). The result is discussed in correlation with the double step superconducting (SC) transition in the specific heat and the multiple SC-phases inferred from the angular dependence of κ.