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Electron Dynamics in high Tc Cuprates; The power of x-rays

Probing the equilibrium and non-equilibrium dynamics of a materials system can yield important clues as to the underlying physics of the material. Here I report two state-of-the-art x-ray scattering experiments that shed new light on the high-Tc superconducting cuprates. In the first, we use inelastic x-ray scattering to measure the spin dynamics in regimes not studied by other techniques. We find antiferromagnetic correlations survive a large range of dopings, tightly constraining magnetism-based theories of superconductivity. In the second experiment, we excite the system with a mid-infra red pulse and follow the dynamics of the charge order. We find it melts within a few hundred femtoseconds, consistent with the time scale on which superconductivity appears in this system. This demonstrates that such charge order competes with superconductivity and is consistent with a modulated ("pair density wave") superconductor.