Universal magnetic properties of ${\mathrm{La}}_{2\mathrm{-}\mathrm{\delta }}$${\mathrm{Sr}}_{\mathrm{\delta }}$${\mathrm{CuO}}_4$ at intermediate temperatures

We present the theory of two-dimensional, clean quantum antiferromagnets with a small, positive, zero temperature (T) stiffness ${\mathrm{\rho }}_5$, but with the ratio ${\mathit{k}}_{\mathit{B}}$T/${\mathrm{\rho }}_{\mathit{s}}$ arbitrary. Universal scaling forms for the uniform susceptibility (${\mathrm{\chi }}_{\mathit{u}}$), correlation length (ξ), and NMR relaxation rate (1/${\mathit{T}}_1$) are proposed and computed in a 1/N expansion and by Monte Carlo simulations. For large ${\mathit{k}}_{\mathit{B}}$T/${\mathrm{\rho }}_{\mathit{s}}$, ${\mathrm{\chi }}_{\mathit{u}}$(T)/T and Tξ(T) asymptote to universal values, while 1/${\mathit{T}}_1$(T) is nearly T independent. We find good quantitative agreement with experiments and some numerical studies on ${\mathrm{La}}_{2\mathrm{-}\mathrm{\delta }}$${\mathrm{Sr}}_{\mathrm{\delta }}$${\mathrm{CuO}}_4$.