Evolution of the pseudogap across the magnet-superconductor phase boundary of Nd2-x Cex Cu O4

The doping dependence of electronic states in an electron-doped high-temperature superconductor (HTSC) Nd2-x Cex Cu O4 was studied by high-resolution angle-resolved photoemission spectroscopy. We observed that the high-energy pseudogap around the hot spot shows an abrupt filling-in at the magnet-superconductor phase boundary, resulting in the unusual reconstruction of the Fermi surface. The magnitude (ΔPG) and the temperature (T*) at which the pseudogap is filled-in show a close relation to the effective hyperfine coupling energy (Jeff) and the spin-correlation length (ξAF), respectively. These results suggest the magnetic origin of the pseudogap and the unconventional nature of the magnet-superconductor phase transition in electron-doped HTSC.