Nuclear quadrupole resonance and heavy-fermion superconductivity inCeCu2Si2

${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ nuclear quadrupole resonance (NQR) has been observed in the ternary compound ${\mathrm{CeCu}}_2$ ${\mathrm{Si}}_2$ which, when stoichiometric, is a heavy-fermion superconductor. In a superconducting specimen ($T_c\simeq 0.6$ K) the observed temperature dependence of the spin-lattice relaxation rate $\frac{1}{T_1\mathrm{}\left(T\right)\mathrm{}}$ is consistent with a conventional quasiparticle excitation spectrum below $T_c$, with a pair-breaking parameter approximately half the value for suppression of superconductivity. Features in $\frac{1}{T_1\mathrm{}\left(T\right)\mathrm{}}$ between $T_c$ and 1.2 K appear to signal a phase transition, possibly structural in nature. NQR data from a nonsuperconducting sample are consistent with extensive disorder in the Cu site occupation.