The NMR relaxation rate of O in undoped Sr₂CuO₂Cl₂: Probing two-dimensional magnons at short distances

Original · EN

We calculate the nuclear relaxation rate of oxygen in the undoped quasi two-dimensional quantum Heisenberg antiferromagnet Sr₂CuO₂Cl₂ above the Neel temperature. The calculation is performed at two-loop order with the help of the Dyson-Maleev formulation of the spin-wave expansion, taking all scattering processes involving two and three magnons into account. At low temperatures T we find 1 / T₁ = c₁ T³ + c₂ T⁴ + O (T⁵), and give explicit expressions for the coefficients c₁ (two-magnon scattering) and c₂ (three magnon scattering). We compare our result with a recent experiment by Thurber et al. and show that this experiment directly probes the existence of short-wavelength magnons in a two-dimensional antiferromagnet.