Electron dynamics in Nd1.85Ce0.15CuO4+δ:: Evidence for the pseudogap state and unconventional c-axis response -: art. no. 224503

Infrared reflectance measurements were made with light Polarized along the a and c axes of both superconducting and antiferromagnetic phases of electron doped Nd1.85Ce0.15CuO4+delta. The results are compared to characteristic features of the electromagnetic response in hole doped cuprates. Within the CuO2 planes the frequency dependent scattering rate, 1/tau(omega), is depressed below similar to 650 cm(-1); this behavior is a hallmark of the pseudogap state. While in several hole doped compounds the energy scales associated wit the pseudogap an superconducting states are quite close, we are able to show that in Nd1.85Ce0.15CuO4+delta the two scales differ by more than one order of magnitude. Another feature of the in-plane charge response is a peak in the real part of the conductivity, sigma (1)(omega), at 50-110 cm(-1) which is in sharp contrast with the Drude-like response where sigma (1)(omega) is centered at omega = 0. This latter effect is similar to what is found in disordered hole doped cuprates and is discussed in the context of carrier localization. Examination of the c-axis conductivity gives evidence for an anomalously broad frequency range from which the interlayer superfluid is accumulated. Compelling evidence for the pseudogap state as well as other characteristics of the charge dynamics in Nd1.85Ce0.15CuO4+delta signal global similarities of the cuprate phase diagram with respect to electron and hole doping.