Evidence for unconventional superconducting fluctuations in heavy-fermion compound CeNi ₂Ge ₂

We present evidence for unconventional superconducting fluctuations in a heavy-fermion compound CeNi ₂Ge ₂. The temperature dependence of the ⁷³Ge nuclear-spin-lattice-relaxation rate 1/T ₁ indicates the development of magnetic correlations and the formation of a Fermi-liquid state at temperatures lower than T _FL = 0.4 K, where 1/T ₁T is constant. The resistance and 1/T ₁T measured on an as-grown sample decrease below T _c ^onset = 0.2 K and T _c ^NQR = 0.1 K, respectively; these are indicative of the onset of superconductivity. However, after annealing the sample to improve its quality, these superconducting signatures disappear. These results are consistent with the emergence of unconventional superconducting fluctuations in close proximity to a quantum critical point from the superconducting to the normal phase in CeNi ₂Ge ₂.