Study on correlation between magnetism and superconductivity in f-electron systems

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We have studied several typical heavy fermion compounds, including Ce-and U-based magnetic superconductors and a Sm-based valence fluctuating material, in terms of thermodynamic, magnetic, and transport measurements together with the neutron scattering technique. We obtained the following results.1. We revealed the spin dynamics of UPd_2Al_3 and UNi_2Al_3, and succeeded in detecting de Haas-van Alphen effect signals for them.2. We obtained a pressure-temperature phase diagram of URu_2Si_2 that exhibits the coexistence of hidden order and superconductivity, and revealed a first order phase line (called Sato line) that separates the hidden and antiferromagnetic ordered states. We also indicated that the superconducting state is destroyed by the antiferromagnetism emerging under pressure.3. We observed that the superconducting transition temperature of UGe_2 exhibits a twin peak structure under pressure. It remains an open question whether the twin peak structure at around two critical pr … More essures implies the existence of two different superconducting regions.4. We found that the superconductivity appears even at ambient pressure for CeRhIn_5. From the pressure dependence of the superconducting transition temperature and Neel temperature, with the help of a theoretical model, we suggested that the superconductivity and antiferromagnetism competitively coexists for a state on the Fermi surface.5. We constructed a pressure-temperature phase diagram of the typical mixed valence compound SmS, and revealed the existence of a pseudogap in the so-called golden phase. This clearly resolves the long-standing discrepancy whether golden SmS is a metal or a semiconductor.We constructed an apparatus for dilatation and dc magnetization experiments under pressure. We also developed a _3He refrigerator using a charcoal pump.As a result, we revealed some aspects of the heavy fermion materials and solved some of fundamental problems in the field of the heavy fermion physics, although the underlying physics remains to be resolved. Less