The S=1/2 spin chain material SrCuO2 doped with 1% S=1 Ni-impurities is studied by inelastic neutron scattering. At low temperatures, the spectrum shows a pseudogap \Delta ~ 8 meV, absent in the parent compound, and not related to any structural phase transition. The pseudogap is shown to be a generic feature of quantum spin chains with dilute defects. A simple model based on this idea quantitatively accounts for the exprimental data measured in the temperature range 2-300 K, and allows to represent the momentum-integrated dynamic structure factor in a universal scaling form.
@article{arxiv.1306.2614,
title = {Spin pseudogap in Ni-doped SrCuO2},
author = {G. Simutis and S. Gvasaliya and M. Mansson and A. L. Chernyshev and A. Mohan and S. Singh and C. Hess and A. T. Savici and A. I. Kolesnikov and A. Piovano and T. Perring and I. Zaliznyak and B. Buchner and A. Zheludev},
journal= {arXiv preprint arXiv:1306.2614},
year = {2013}
}