Evidence for unconventional superconducting fluctuations in heavy-fermion compound CeNi2Ge2

TL;DR

This study provides evidence for unconventional superconducting fluctuations near a quantum critical point in the heavy-fermion compound CeNi2Ge2, with superconducting signatures sensitive to sample quality.

Contribution

It demonstrates the presence of unconventional superconducting fluctuations in CeNi2Ge2 and shows their dependence on sample annealing, advancing understanding of quantum criticality in heavy-fermion systems.

Findings

Superconducting signatures appear below 0.2 K in as-grown samples.

Annealing suppresses superconducting signatures, indicating their fragile nature.

Magnetic correlations develop below 0.4 K, suggesting proximity to a quantum critical point.

Abstract

We present evidence for unconventional superconducting fluctuations in a heavy-fermion compound CeNi$_2$Ge$_2$. The temperature dependence of the $^{73}$Ge 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 $T_{\rm FL}=0.4$ K, where $1/T_1T$ is constant. The resistance and $1/T_1T$ measured on an as-grown sample decrease below $T_{\rm c}^{\rm onset} = 0.2$ K and $T_{\rm c}^{\rm NQR} = 0.1$ 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$_2$Ge$_2$.