Evidence for a common high-temperature superconducting effect in La1.85Sr0.15CuO4 and YBa2Cu3O7.

Abstract

We report the positron-annihilation lifetime and Doppler-broadening energy spectra in ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ superconductors for 10<T<297 K. A strong temperature dependence in positron lifetime and momentum distribution parameters is observed for positron-electron annihilation data while the sample is in the superconducting state, but not while it is in the normal state. We show experimental evidence that the superconducting mechanisms in ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ are similar and suggest that this is a consequence of a common physics involving the delicate balance between localized and itinerant-electron behavior.