LUTTINGER FERMI-SURFACE OF METALLIC GAP SPECTRAL WEIGHT IN ND1.85CE0.15CUO4-Y

Angle-resolved photoemission measurements for bulk single crystals of Nd2-xCexCuO4-y with x = 0.15 show that the spectral weight which build s in the gap of the x = 0 insulator displays a Luttinger Fermi surface , the first such observation for a material which is electron doped an d which must be driven metallic by alloying. This finding greatly stre ngthens our previous conclusion that the metal's chemical potential li es in gap-filling spectral weight, and sharpens the distinction betwee n theories in which this does or does not occur.