Robust intrinsic superconducting phases in underdoped LSCO single crystals

We have measured the superconducting critical temperature ( T C ) and the diamagnetic susceptibility of La2−xSrxCuO4 single crystals in various magnetic fields. We observed a field-induced evolution from an apparent T C phase to an intrinsic T C 1 = 15 K or T C 2 = 30 K phase characterized by “magic” hole concentration which is commensurate with that of a two-dimensional electronic lattice. The onset T C of the intrinsic superconducting phases remains robust up to H = 5 T . We suggest that the intrinsic superconducting phases at “magic” doping concentrations are the pristine electronic phases of high temperature superconductors.