Nuclear Magnetic Resonance and Heavy-Fermion Superconductivity in Ube13 and CeCu2Si2

Cheng Tien

《Chinese Journal of Physics》 26卷1S期 (1988/02) Pp. 54-70

並列摘要

Nuclear magnetic resonance (NMR) experiments have been carried out in two heavy fennion superconductors, CeCu2Si2 and U1-xThxBe13(x=0,0.0331).In one or our CeCu2Si2 superconducting specimens, the observed temperature dependence of the spin-lattice relaxation rate l/T, (T) is consistent with a conventional quasiparticle excitation spectrum below the superconducting transition temperature T,. In the other superconducting CeCu2Si2 sample, the nuclear spin-lattice relaxation rate decreases drastically just below Tc without the apparent enhancement observed in the first sample. This lack of enhancement in 1/T1 (T) suggests that the superconductivity in CeCu2Si2 is not due to a conventional mechanism. Some unusual features in 1/T1(T) between Tc and 1.2 K appear to signal a phase transition, possibly structural in nature. .NQR measurements of the non-superconducting CeCu2Si2 sample are consistent with extensive disorder in the Cu site occupation.The spin-lattice relaxation rate in UBe13 varies approximately as T3 well below the transition temperature Tc. This behavior is consistent with a class of anisotropic pairing models for which the superconducting gap vanishes along lines on the Fermi surface.Two phase transitions have been observed in the specific heat measurements of U0.9669Th0.0331Be13 at Tc1 and Tc2 For Tc2 ＜ T＜ Tc1, 1/T1 varies less rapidly than T For 0.1 K ＜ T ＜ Tc2 1/T1 varies as T^3, which suggests that the nature of the superconductivity of U0.9669 Th0.0331Be13 in this temperature range is the same as that of UBe13