Critical spin dynamics of the 2D quantum Heisenberg antiferromagnets Sr2CuO2Cl2 and Sr2Cu3O4Cl2

We report a neutron scattering study of the long-wavelength dynamic spin co rrelations in the model two-dimensional S = 1/2 square lattice Heisenberg a ntiferromagnets Sr2CuO2Cl2 and Sr2Cu3O4Cl2. The characteristic energy scale , omega (0)(T/J), is determined by measuring the quasielastic peak width in the paramagnetic phase over a wide range of temperature (0.2 less than or similar to T/J less than or similar to 0.7). The obtained values for omega (0)(T/J) agree quantitatively between the two compounds and also with value s deduced from quantum Monte Carlo simulations. The combined data show scal ing behavior, omega similar to xi (-z), over the entire temperature range w ith z = 1.0(1), in agreement with dynamic scaling theory.