Unconventional Heavy-Fermion Superconductivity of a New Transuranium Compound NpPd_5Al_2(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We succeeded in growing a new transuranium compound NpPd_5Al_2 with the tetragonal crystal structure by the Pb-flux method, and measured the electrical resistivity, specific heat, magnetic susceptibility and magnetization. NpPd_5Al_2 is found to be a paramagnetic heavy-fermion superconductor with strong coupling ΔC/γT_c=2.33 [T_c=4.9K and γ=200mJ/(K^2・mol)]. The upper critical field H_<c2> at 0K is large and highly anisotropic: H_<c2>(0)=37kOe for H‖[100] and H_<c2>(0)=143kOe for H‖[001]. H_<C2> is found to be strongly suppressed by the magnetic field, and the magnetization curve indicates a step-like increase at H_<C2>, which are due to the paramagnetic effect. The low-temperature electronic specific heat approximately follows the T^3-dependence, indicating the existence of point nodes in the energy gap. The d-wave superconductivity with point nodes is most likely realized in this compound.
社団法人日本物理学会の論文
2007-06-15