Field-induced staggered magnetization near impurities in the S= one-dimensional Heisenberg antiferromagnetSr2CuO3

We report an impurity effect in the spin- one-dimensional Heisenberg antiferromagnet ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_3$. The ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ NMR spectra develop a broad background with sharp edges at low temperatures. The anisotropy and the temperature dependence of this structure indicate that the external magnetic field induces local staggered magnetization near impurities, whose spatial extent grows with decreasing temperature. The results are in good agreement with the theoretical prediction by Eggert and Affleck for a semi-infinite spin chain with an open end.