Spin pseudogap in Ni-doped SrCuO2

Abstract

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 ∆ ≈ 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.