Kondo effect on Nucler Quadrupole Interaction

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PrPt5 is a hyperfine enhanced nuclear magnet. By specific heat measurement, Nuclear magnetic ordering was observed at 2mK. Furthermore, we observed a strongly enhanced nuclear quadrupole interaction of about 6mK. Owing to the large nuclear quadrupole interaction, we can study the effect of nuclear quadrupole interaction on resistance at rather higher temperature range of mK. To our's surprise, PrPt5 with Pt impurity phase became superconductivity. Then, we study on the coexistence of nuclear ferromagnetism and type-II superconductivity in PrPt5 with Pt impurity phase. It exhibits superconductivity at Ts=213 mK in zero field and a remarkable suppression (but finite) of the upper critical field Hc2 below a ferromagnetic nuclear ordering temperature (Tc〜2 mK). The lower critical field Hc1(〜1mT) is suppressed to 0.5mT by the presence the ferromagnetic order. The spontaneous nuclear magnetization coexists with superconductivity of Type II at field lager than 1mT down to the lowest measured temperature of 0.2 mK. At zero field, we think that a Domain-like magnetic state discussed by M.L.Kulic, A.I.Buzdin and L.N.Bulaevskii co-exists with the Meissner state. However, In a single phase sample of PrPt5, a superconductivity was not observed. We do not know the reason. We also study P-wave superconductor and a hyperfine enhanced nuclear magnet PrOs4Sb12. But nuclear magnetic ordering was not observed down to 0.2 mK.