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Abstract:
Various types of ground states in strongly correlated electron systems
have been systematically investigated by means of NMR/NQR at low
temperatures under high magnetic field and pressure. We focus on two
well-known heavy-electron families, CeCu 2X 2 (X=Si and Ge) (Ce(122))
and UM 2Al 3 (M=Ni and Pd) (U(123)). The Cu NQR experiments on CeCu 2X 2
under high pressure indicate that the physical property of CeCu 2Ge 2 at
high pressure, i.e. above the transition at 7.6 GPa from
antiferromagnetic (AF) to superconductivity, are clearly related to that
of CeCu 2Si 2 at ambient pressure. In addition to the H-T phase diagram
established below 7 T, NMR and specific heat experiments on polycrystal
CeCu 2.05Si 2 have revealed the presence of a new phase above 7 T. In a
high-quality polycrystal of UPd 2Al 3 with a record high-T c of 2K at
ambient pressure and the narrowest Al NQR line width, the nuclear-spin
lattice relaxation rate, 27(1/T 1) measured in zero field has been
found to obey the T 3 law down to 0.13 K, giving strong evidence that
the energy gap vanishes along lines on the Fermi surface. Thus it seems
that all heavy-electron superconductors exhibit lines of zero gap,
regardless of their different magnetic properties.
