The normal-conducting state of the superconductor ${\mathrm{UTe}}_2$ is studied by entropy analysis for magnetic fields along the $b$ axis, obtained from magnetization using the relation ${(\partial M/\partial T)}_B={(\partial S/\partial B)}_T$. We observe a strong increase in entropy with magnetic field due to metamagnetic (MM) fluctuations (spatially uniform, $Q=0$). The field dependence is well described by the Hertz-Millis-Moriya theory for quantum criticality of itinerant MM. Notably, the lower bound of the quantum-critical region coincides well with the position of the minimum in the superconducting transition temperature $T_c\left(B\right)$. Hence, our results suggest that $Q=0$ fluctuations reinforce the superconductivity.

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• Quantum criticality
• Spin fluctuations
• Spin-triplet pairing
• Ferromagnetic superconductors
• Heavy-fermion systems
• Unconventional superconductors