The low energy magnetic excitation spectrum of the Heisenberg antiferromagnetic S=1/2 chain system Sr2CuO3 with Ni- and Ca-impurities is studied by neutron spectroscopy. In all cases, a defect-induced spectral pseudogap is observed and shown to scale proportionately to the number of scattering centers in the spin chains.
@article{arxiv.1611.04183,
title = {Spin pseudogap in the $S=\frac{1}{2}$ chain material Sr$_2$CuO$_3$ with impurities},
author = {G. Simutis and S. Gvasaliya and N. S. Beesetty and T. Yoshida and J. Robert and S. Petit and A. I. Kolesnikov and M. B. Stone and F. Bourdarot and H. C. Walker and D. T. Adroja and O. Sobolev and C. Hess and T. Masuda and A. Revcolevschi and B. Büchner and A. Zheludev},
journal= {arXiv preprint arXiv:1611.04183},
year = {2017}
}