Time-resolved optical reflectivity of the electron-doped Nd _2-xCe_xCuO_4+δ Cuprate superconductor: Evidence for an interplay between competing orders

We use pump-probe spectroscopy to measure the photoinduced reflectivity ΔR of the electron-doped cuprate superconductor Nd_2-xCe _xCuO_4+δ at a value of x near optimal doping, as a function of time, temperature, and laser fluence. We observe the onset of a negative ΔR signal at T^*≈75 K, above the superconducting transition temperature, T_c, of 23 K. The relatively slow decay of ΔR, compared to the analogous signal in hole doped compounds, allows us to resolve time-temperature scaling consistent with critical fluctuations. A positive ΔR signal onsets at T_c that we associate with superconducting order. We find that the two signals are strongly coupled below T_c, in a manner that suggests a repulsive interaction between superconductivity and another fluctuating order.