Extended string order parameter in the (S = 1,1/2) mixed spin chain

• Published in: Journal of the Physical Society of Japan 2007-08, Vol.76 (8), p.84714
• Main Authors: TONOOKA, Shun, NAKANO, Hiroki, KUSAKABE, Koichi, SUZUKI, Naoshi
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Critical-point effects, specific heats, short-range order; Exact sciences and technology; General theory and models of magnetic ordering; Magnetic properties and materials; Physics; Spin chain models; Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
• ISSN: 0031-9015; 1347-4073
• DOI: 10.1143/jpsj.76.084714

We have found a set of order parameters that characterize the plateau state of the (S=1,1/2) spin chain system. The order parameters are regarded as extensions of the string order parameter of the S=1 antiferromagnetic Heisenberg spin chain. The extension is made by mapping the Sz=1/2 (Sz=-1/2) state of an S=1/2 spin onto the Sz=0 (Sz=-1) state of an S=1 spin. Numerical data indicate that, when single-ion anisotropy D is introduced, all the order parameters decrease continuously and vanish in the large-D region. Our estimate of the critical value Dc for the phase transition agrees well with the phase boundary determined by a previous level spectroscopy analysis. We present estimates of three critical exponents that are associated with the order parameters. A scaling relation between the exponents holds well in the present system.