A. Missiaen, H. Mayaffre, D. LeBoeuf, M.-H. Julien, Laboratoire des Champs Magnétiques Intenses, Grenoble, France
S. Pyon, Department of Applied Physics, University of Tokyo, Japan
T. Takayama and H. Takagi, Max Planck Institute for Solid State Research, Stuttgart, Germany


A recent NMR and ultrasound study of the cuprate superconductor La_2-xSr_xCuO₄ [Frachet et al. Nat. Phys. 16, 1064 (2020)] revealed that p* ~ 0.19, the critical hole doping for the pseudogap phase at T = 0, coincides with a quantum phase transition from frozen to fluctuating antiferromagnetism, once superconductivity has been quenched in high magnetic fields. Here, we present ¹³⁹La nuclear magnetic resonance (NMR) measurements of the temperature, magnetic field and hole-doping dependence of spin fluctuations in the sister compound La_1.8-xEu_0.2Sr_xCuO₄. We find similar field-dependent glassy freezing as in La_2-xSr_xCuO₄, up to a doping ~ 0.24, consistent with p* for La_1.8-xEu_0.2Sr_xCuO₄. That the specific heat (measured in high magnetic fields) is sharply enhanced around the same doping in this material [Michon et al., Nature 567, 218 (2019)], suggests that the two observations are connected, one way or another.