Infrared properties of electron-doped cuprates: Tracking normal-state gaps and quantum critical behavior in Pr2 − xCexCuO4

We report the temperature dependence of the infrared-visible conductivity of Pr2 − xCexCuO4 thin films. When varying the doping from a non-superconducting film (x = 0.11) to a superconducting overdoped film (x = 0.17), we observe, up to optimal doping (x = 0.15), a partial gap opening. The magnitude of this gap extrapolates to zero for x ~ 0.17. A model combining a spin density wave gap and a frequency- and temperature-dependent self-energy reproduces our data reasonably well, suggesting the coexistence of magnetism and superconductivity in this material and the existence of a quantum critical point at this Ce concentration.