Spin Pseudogap in Ni-Doped SrCuO$_2$

Effect of spin-1 impurities on the spectrum of an archetypical Heisenberg antiferromagnetic spin-$\frac{1}{2}$ chain SrCuO$_2$ is studied by inelastic neutron scattering [1]. We find that a spin pseudogap appears in the spectrum upon introduction of the impurities. We show that the pseudogap is a generic feature of quantum spin chains with dilute defects. This allows us to express the dynamic structure factor in a universal scaling form even for the system with fragmented chains. A simple model based on chain fragmentation shows good quantitative agreement with the experimental data for a broad temperature range.\\[4pt][1] Simutis et al, PRL 111, 067204 (2013)