Quantum Fluctuations in the Frustrated Antiferromagnet Sr2Cu3O4Cl2

Abstract Sr2Cu3O4Cl2 is an antiferromagnet consisting of weakly coupled CuO planes which comprise two weakly interacting antiferromagnetic subsystems, I and II, which order at respective temperatures TI ≈ 390K and TII ≈ 40K. Except asymptotically near the ordering temperature, these systems are good representations of the two-dimensional quantum spin 1/2 Heisenberg model. For T < TII there are four low-energy modes at zero wave vector, three of whose energies are dominated by quantum fluctuations. For TII < T < TI there are two low energy modes. The mode with lower energy is dominated by quantum fluctuations.