Low-Energy Excitations Around (pi/2, pi/2) Points in the Pseudogap Phase of Nd1.85 Ce0.15 CuO4

Polarized electronic Raman scattering of the electron doped superconductor Nd 1.85 Ce0.15Cu04 (Tc=22K) reveals the formation of a pseudogap below a characteristic temperature T* 220K and energy Eg* = 850 cm -1. The suppression of the spectral weight is more pronounced in the nodal directions of k-space. Below T* we observe low frequency quasi-elestic scattering that is consistent with emergence of long-lived excitations in the proximity of the (pi/2, pi/2) points. These excitations do not contribute to optical conductivity and could be responsible for the Wiedemann-Franz law violation.