Quantum criticality might underlie the anomalous properties of strange metals and may play a central role in the emergence of unconventional superconductivity. In cuprate superconductors, this scenario has been debated for decades, with key signatures including a logarithmic divergence of the electronic specific heat [1], a drop in carrier density revealed by the Hall effect [2], and evidence for Fermi surface reconstruction from angle-dependent magnetoresistance (ADMR) [3]. Despite this extensive body of work, the existence and nature of a quantum critical point (QCP) at the end of the pseudogap phase remain unsettled.

Superconducting infinite-layer nickelates provide a new platform to revisit this question. These materials exhibit striking similarities with cuprates, including nodal superconductivity [4], a strange-metal regime with $T$-linear resistivity [5], and a pronounced change in the Hall coefficient across a critical doping [5]. However, their thin-film nature precludes direct thermodynamic probes such as specific heat and limits access to Fermi surface information via ADMR, leaving the presence of a QCP unresolved.

Here we use the Seebeck coefficient as a proxy for entropy per carrier to probe quantum criticality in La$_{1-x}$Sr$_x$NiO$_2$. At the critical doping $x^\star$ marking the onset of $T$-linear resistivity, we observe a logarithmic divergence of the Seebeck coefficient upon cooling, $S/T \propto \log(T)$, once superconductivity is suppressed by a high magnetic field [6]. This behavior provides a direct thermodynamic signature of a QCP. In addition, analysis of the Hall effect reveals a drop in carrier density across $x^\star$, consistent with a reconstruction of the Fermi surface and the emergence of a pseudogap-like phase at lower doping.

These results establish a quantum critical point at the boundary of a pseudogap-like phase in infinite-layer nickelates, supporting a unified picture in which quantum criticality governs strange-metal behavior across strongly correlated superconductors.

References
[1] Michon et al. Nature 567, 218 (2019)
[2] Badoux et al. Nature 531, 210 (2016)
[3] Fang et al. Nature Physics 18, 558 (2022)
[4] Ranna et al. PRL 135, 126501 (2025)
[5] Lee et al. Nature 619, 288 (2023)
[6] Iorio-Duval et al. arXiv:2510.12786