Interaction of itinerant electrons and spin fluctuations in electron-doped cuprates

We performed angle-resolved photoemission and optical studies on electron-doped high-temperature superconductors (HTSCs), and compared the results with various theoretical models. Based on the fit to the experimental data, we conclude that itinerant electrons in the nonmagnetic phase predominantly couple to the phase fluctuations of the remnant antiferromagnetic (AF) order, rather than to the spin excitations derived from particle-hole pairs. Our observation naturally accounts for the pseudogap phenomenon and other experimental facts in electron-doped HTSCs in terms of the size of the remnant moment and the AF-correlation length. We propose a microscopic model based on the phase fluctuation scenario which leads to a d-wave pairing gap.