Anomalous lattice dynamics in superconducting La_1.84Sr_0.16CuO₄

Although Lanthanum-based cuprates represent the first discovered high-T_c superconductors, they are still not fully understood, with even their microscopic lattice structures still under debate. There a variety of different orders coexist, favoring one structure over the other, partially even competing with superconductivity. Here, we present recent x-ray photon correlation spectroscopy measurements on optimally-doped La_1.84Sr_0.16CuO₄ which probes slow lattice dynamics. A rapid change in lattice dynamics and speckle contrast entering the superconducting state are shown, indicating a change from slower, cascade-like relaxation towards faster, more localized lattice relaxation with fluctuations driven by superconducting order. This underpins the influence of the superconductivity on the lattice stability and suggests an even higher importance of electron-lattice coupling than previously considered.