Terahertz spectroscopy of electron-doped superconductors in magnetic field

In the terahertz and infrared regions we measured the optical conductivity and penetration depth of the electron-doped cuprate superconductor La2-xCexCuO4. In the frequencytemperature behavior of conductivity we observe remarkable differences between the samples with different Ce content, suggesting the gap anisotropy to be a function of the doping level. At terahertz frequencies, we performed measurements in high magnetic fields to suppress superconductivity below Tc. From the conductivity spectra we extract the quasiparticle scattering rate as a function of temperature, and compare its behavior in the superconducting and normal states below Tc. We find a small but measurable optical magnetoresistance at all doping levels, and no signatures for the pseudogap. We also discuss the applicability of ‘universal scaling laws’ to our data on conductivity and penetration depth.