Photoemission study of excess oxygen-doped La2CuO4.10

We have studied excess oxygen-doped La2CuO4.10 (LCO) by angle-resolved photoemission spectroscopy (ARPES) and temperature-dependent angle-integrated photoemission spectroscopy (AIPES). The observed Fermi surface and flat-band position are similar to those of optimally-doped to slightly-underdoped La2−xSrxCuO4 (LSCO). We have observed a large pseudogap of ∼70 meV in the temperature-dependent AIPES spectra, which is larger than that reported for optimally-doped LSCO (∼35 meV). From comparison of low-temperature AIPES spectra between different cooling rates, oxygen disorder is found to cause spectral weight transfer from higher binding energy to near EF and to make the spectral line shapes resemble those of LSCO. This explains the reduction of the large pseudogap in LSCO.