A quantum critical point (QCP) represents a continuous phase transition at absolute zero. In unconventional superconductors, enhanced superconducting transition temperature and magnetic fluctuation strength are often observed together, indicating magnetism-mediated superconductivity. This raises the question of whether quantum fluctuations in other degrees of freedom, such as charge, could similarly boost superconductivity. However, because charge is frequently intertwined with magnetism, isolating and understanding its specific role in Cooper pair formation pose a significant challenge. Here, we report persistent charge density fluctuations (CDFs) down to 15 K in the nonmagnetic superconductor ${\mathrm{Sr}}_{0.77}{\mathrm{Ba}}_{0.23}{\mathrm{Ni}}_2{\mathrm{As}}_2$, which lie near a proposed nematic QCP associated with a sixfold enhancement of superconductivity. Our results show that the quasielastic CDFs do not condense into resolution-limited Bragg peaks but, rather, display nonsaturated strength. The phonons associated with CDFs completely soften at 25 K, with their critical behavior described by the same mathematical framework as the antiferromagnetic Fermi liquid model, yielding a fitted Curie-Weiss temperature of $\theta \approx 0\mathrm{K}$. Additionally, we find that the nematic fluctuations are weakly coupled to the lattice, as evidenced by the absence of softening in nematic-coupled in-plane transverse acoustic phonons. Our discovery positions ${\mathrm{Sr}}_x{\mathrm{Ba}}_{1-x}{\mathrm{Ni}}_2{\mathrm{As}}_2$ as a promising candidate for charge-fluctuation-driven superconductivity.

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• Charge density waves
• Phonons
• Quantum criticality
• Superconductors
• Nonresonant inelastic x-ray scattering