Evidence for antiferromagnetic interactions in the high-temperature superconductorLa1.85Sr0.15CuO4−y

Abstract

Hyperfine specific-heat measurements in superconducting ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4-y}$ strongly suggest the existence of a hyperfine field at the copper nuclei. This field is even larger in undoped and semiconducting ${\mathrm{La}}_2$Cu${\mathrm{O}}_4$ and is compatible with antiferromagnetic order in that compound. We speculate that mobile ${\mathrm{Cu}}^{3+}$ holes in the Sr-doped samples stabilize a fluctuating antiferromagnetic state which at the same time is superconducting.