Interplay of structural and electronic phase separation in single-crystalline La₂CuO_4.05 studied by neutron and Raman scattering

We report a neutron- and Raman-scattering study of a single crystal of La₂CuO_4.05 prepared by high-temperature electrochemical oxidation. Elastic neutron-scattering measurements show the presence of two phases, corresponding to the two edges of the first miscibility gap, all the way up to 300 K. An additional oxygen redistribution, driven by electronic energies, is identified at 250 K in Raman scattering (RS) experiments by the simultaneous onset of two-phonon and two-magnon scattering, which are fingerprints of the insulating phase. Elastic neutron-scattering measurements show directly an antiferromagnetic ordering below a Néel temperature of T_N=210K. The opening of the superconducting gap manifests itself as a redistribution of electronic Raman scattering below the superconducting transition temperature, T_c=24K. A pronounced temperature-dependent suppression of the intensity of the (100) magnetic Bragg peak has been detected below T_c. We ascribe this phenomenon to a change of relative volume fraction of superconducting and antiferromagnetic phases with decreasing temperature caused by a form of a superconducting proximity effect.