A study of the 15K super conducting transition in La2CuO4+delta

Two superconducting transitions occurred at similar to 30K and similar to 1 5K in La2CuO4+delta near a specific hole concentration corresponding to P-s = 1/8. At this hole concentration P-s the Meissner signal size (chi (M)) o f 30K transition diminished while that of the 15K transition remained essen tially constant. Therefore, only a 15K transition existed at P-s. Tills 15K state was so delicate that a small increase of hole concentration by Delta P=0.0026 resulted in a T-c shift by similar to 5K. We suggest that this uni que 15K state at P-s is a result of "global" minimization of free energy th rough electronic phase separations involving localization/condensation of d oped holes.