MICROSCOPIC PHASE-SEPARATION IN LA2CUO4+X INDUCED BY THE SUPERCONDUCTING TRANSITION

The phase separation (PS) effect in superconducting La2CuO4+x (x less than or equal to 0.04) single crystals with low oxygen mobility was st udied via mu SR spectroscopy, high-resolution neutron diffraction, and magnetic susceptibility. Despite the fact that all crystals are insid e the miscibility gap (0.01<x<0.06), only crystals with a sufficiently large excess oxygen concentration x=0.04 show a macroscopic phase sep aration according to the neutron-diffraction data. However, in all sam ples a phase transition to an ordered magnetic state was observed by m u SR spectroscopy concomitantly with the onset of superconductivity. T his effect is treated as a microscopic phase separation which is possi bly driven by superconductivity. [S0163-1829(98)02341-8].