Strange metal phase ending with spin freezing in a cuprate superconductor

Strange metals – which exhibit unusual properties such as a resistivity that scales linearly with temperature – challenge our understanding of charge transport in metals. Here, we investigate how the strange metal phase of La_{2 -x}Sr_xCuO₄ is impacted by a field-induced glassy antiferromagnetic state. Using magnetic fields above 80 T, we discover a strong enhancement of the normal state magnetoresistance when entering the antiferromagnetic glass phase. We demonstrate that the spin glass causes insulating-like upturns in the resistivity inside the pseudogap phase, which resolves the origin of the crossover from metal to insulator. In addition, the strange metal phase appears at low temperatures over an extended range of magnetic fields where magnetic moments fluctuate, and disappears when these moments freeze out. We conclude that the transport properties of the strange metal phase are closely linked to low energy magnetic fluctuations that persist at the lowest temperatures.