Cu nuclear quadrupole resonance and relaxation on the Yb-based heavy-fermion compound YbCu5

Cu nuclear quadrupole resonance (NQR) study has been performed on a heavy-f ermion compound cubic YbCu5 which has a large electronic specific heat coef ficient of gamma = 550 mJ/mol K-2. Cu-63 and Cu-65 NQR spectra confirmed th at magnetic ordering is absent in cubic YbCu5 at least down to 1.6 K. Cu-63 nuclear magnetic relaxation rate (1/T-1) of cubic YbCu5 shows Korringa rel ation where 1/T-1 T = const below 4.2 K, indicating the evolution of Fermi- liquid state. With increasing temperature above 50 K, the 4f-electron contr ibution to 1/T-1, (1/T-1)(4f), tends to be saturated to a constant value, i mplying that 4f electrons are localized with magnetic moments. The temperat ure dependence of (1/T-1)(4f) can be qualitatively explained by the tempera ture dependence of the 4f-electron correlation rates (tau(4f))(-1), calcula ted within the impurity Kondo model. [S0163-1829(99)07017-4].