Spin Excitations in the Square-Lattice Heisenberg Model with Ring-Exchange Interactions

An exact-diagonalization technique on small clusters is used to study the low-energy excitations of the antiferromagnetic Heisenberg model with the ring-exchange interaction. We in particular focus on the one-magnon dispersion relation along the border of the antiferromagnetic Brillouin zone and discuss the role of the ring-exchange interaction in the spin excitations observed in La2CuO4. We also discuss the low-energy excitations of Sr2IrO4 observed recently by a resonant inelastic X-ray scattering experiment, thereby suggesting possible importance of the ring-exchange interactions in this system as well.

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