O17 NMR study of the inhomogeneous electronic state in La2−xSrxCuO4 crystals

We report measurements on the inhomogeneous line broadening of the O17 NMR spectrum in the high Tc superconductor La2−xSrxCuO4 for single crystals with nominal hole concentrations x=0.035, 0.05, 0.07, 0.115, and 0.15. A substantial overlap between the O17 NMR spectrum of different crystals is reported, and the extent of the overlap is shown to increase with decreasing temperature. The spin-lattice relaxation rate divided by temperature, 1∕T117T, is found to vary linearly with frequency (or Knight shift Kspin17, equivalently) across the O17 NMR spectrum of each crystal, with the same scaling form given by 1∕T117T=βKspin17, where β=2.4(2)(sK%)−1. We therefore argue that the overlap between the O17 NMR spectrum of different crystals x is a result of an inherent spatial variation in hole concentration within each crystal, and that the extent of the line broadening, Δ17Kspin, is a measure of the extent Δ17xlocal (or amplitude) of the spatial variation in local hole concentration, xlocal17=x±Δ17xlocal. We successfully fit the O17 NMR line shapes with a simple numerical model that determines the random distribution in local hole concentration xlocal17 as a result of the random spatial distribution in Sr2+ hole donors within a patch radius Rpatch17. We find that Rpatch17=2–5nm best fits the data, implying a short length scale for the inhomogeneous electronic state. In this report we present the first systematic study of the spatial distribution in the local static spin susceptibility in the high Tc cuprates.