Structures and incommensurate spin excitations in excess oxygen-doped La 2CuO 4+ y

Abstract

Over the past decade, we have studied in detail the low-energy spin fluctuations in :a 2− x Sr x CuO 4 for x between 0 and 0.18. Our experiments, as well as those by others, have revealed a fascinating interplay between the hole doping, the static and dynamic spin fluctuations and superconductivity. Recently, using electrochemical techniques, we have learned how to produce large single crystals of La 2CuO 4+ y which are relatively homogenous. In this latter system, the dopants are characterized by annealed rather than quenched disorder. Furthermore, we have demonstrated staging behavior of the excess oxygen analogous to staging in intercalated graphite. We have now succeeded in carrying out measurements of the low-energy spin fluctuations in stage-6 La 2CuO 4+ y . Specifically, we find that in this system which has T c = 31 K, the spin fluctuations are incommensurate with energy and temperature dependencies very much like those in La 1.85Sr 0.15CuO 4 with T c = 33 K. In addition, we find that T c/ δ is a constant for high-quality materials in both La 2− x Sr x CuO 4 and La 2CuO 4+ y , here δ is the incommensurability.