Quantum critical behavior of cuprate superconductors observed by inelastic X-ray scattering

The authors present resonant inelastic X-ray scattering measurements of the cuprate superconductor La2−xSrxCuO4, observing a quantum-critical scaling collapse. From the critical exponent, they argue that the symmetry of the quantum critical point is enlarged from O(2) to O(4), implying that orders beyond just the charge density wave participate.