Effect of heat treatment on electronic phase in underdoped La2-xSrxCuO4 single crystal

Superconducting La_2-xSr_xCuO₄ crystals grown bythe travelling-solvent floating-zone technique were thermally treatedunder various temperatures and oxygen pressures for moderatelyadjusting the oxygen content. The response of intrinsic electronicproperty of the crystals to the change of hole density in La_2-xSr_xCuO₄ in the vicinity of the magic doping of x =1/16 (=0.0625) is studied in detail by magnetic measurements undervarious fields up to 1,T. It is found that when the superconductingcritical temperature (T_{rm C}) increases with the oxygen content,there appears also a new subtle electronic state that can be detectedfrom the differential curves of diamagnetic susceptibilityd$chi$/d$T$ of the crystal sample. In contrast with the intrinsicstate, the new subtle electronic state is very fragile under themagnetic fields. Our results indicate that a moderate change inoxygen doping does not significantly modify the intrinsic electronicstate originally existing at the magic doping level.