Mixed-spin systems: coexistence of Haldane gap and antiferromagnetic long range order

Abstract

Recent experiments on the quasi-1D antiferromagnets $R_{2}BaNi{O}_5$ (R = rare earth) have shown the existence of purely 1D Haldane gap excitations propagating on the Ni chains. Below an ordering temperature, the gap excitations survive and coexist with the conventional spin waves in the ordered phase. We construct a model mixed-spin system in 2D for which the ground state can be exactly specified. Using the Matrix Product Method, we show the existence of Haldane gap excitations in the ordered phase. We consider different cases of ordering to study the effect of ordering on the degeneracy of the Haldane gap excitations.

13 pages, LaTeX, 2 Postscript figures, communicated to Phys. Rev. B

References in corpus (1)

• Coexistence of Haldane gap excitations and long range antiferromagnetic order in mixed-spin nickelates R_2 Ba Ni O_5

Cited by in corpus (3)

• Magnetic Double Structure for S=1, 1/2 Mixed-Spin Systems
• Anomalous percolation and quantum criticality in diluted rare-earth nickelates
• Quantum and classical dynamics in complex one-dimensional antiferromagnets