Ultrafast time-resolved x-ray scattering reveals diffusive charge order dynamics in La2-xBaxCuO4

Charge order is universal among high-Tc cuprates but its relation to super-conductivity is unclear. While static order competes with superconductivity,dynamic order may be favorable and even contribute to Cooper pairing. Using time-resolved resonant soft x-ray scattering at a free electron laser, we show that the charge order in prototypical La2–xBaxCuO4 exhibits transverse fluctuations at ps timescales. These sub-meV excitations propagate by Brownian-like diffusion and have an energy scale remarkably close to the superconducting Tc. At sub-meV energy scales, the dynamics are governed by universal scaling laws defined by propagation of topological defects. Our results show that charge order in La2–xBaxCuO4 exhibits dynamics favorable to the in-plane superconducting tunneling, and establish time-resolved x-rays as a means to study excitations at energy scales inaccessible to conventional scattering techniques.