New Development of Heavy Electron Systeme including Transuranium Compound

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We grew fifty kinds of rare earth compounds and twenty kinds of uranium and transuranium compounds and studied Fermi surface properties, magnetism and superconductivity for these compounds. Experimental results are summarized as follows :(1) The electronic state of antiferromagnets CeRhIn_5 and CeIn_5 was studied by the de Haas-van-Alphen (dHvA) experiment as a function of pressure P, where the Ne'el temperature T_N becomes zero at the critical pressure P_c: T_N → 0 at P → P_c. We clarified experimentally that the 4f - localized electronic state is changed into the 4f - itinerant one at P_c = 2.35GPa, revealing the first-order phase transition.(2) We discovered pressure-induced superconductivity for CeNiGe_3, Ce_2Ni_3Ge_5, CeIrSi_3 and Ulr. Interesting superconducting properties are observed especial in CeIrSi_3 and UIr without inversion symmetry in the crystal structure. For example, an antiferromagneitic states of CeIrSi_3 becomes superconductive around 2 GPa. Surprisingly, a large upper critical field of about 40T is found at 2.6 GPa when the magnetic field is applied to the tetragonal [001] direction. There is a possibility that spin-triplet superconductivity is realized for H//[001] in CeIrSi_3.(3) We also discovered superconductivity in NpPd_5Al_2 with the transition temperature T_sc = 5K Moreover, we succeeded in detecting the dHvA escillations in transuranium compounds of NpGe_3 and PuIn_3, indicating that 5f electrons in these compounds are itinerant.Our seven papers published in J. Phys. Soc. Jpn. were selected as Editor's Choice, and "A Drastic Change of the FermiSurface at a Critical Pressure in CeRhIn_5: dHvA Study under Pressure, H. Shishido, R. Settai, H. Harima and Y. Onuki:J. Phys. Soc. Jpn. 74 (2005) 1103-1106." was selected as" 13th J. Phys. Soc. Jpn. Paper Award ".