The spin-half XXZ antiferromagnet on the square lattice revisited: A high-order coupled cluster treatment

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS

卷:428

Article

Bishop, R. F.¹  Li, P. H. Y.¹  Zinke, R.²  Darradi, R.²  Richter, J.²  Farnell, D. J. J.³  Schulenburg, J.⁴ 

[1] Univ Manchester, Sch Phys & Astron, Schuster Bldg, Manchester M13 9PL, Lancs, England

[2] Otto von Guericke Univ, Inst Theoret Phys, POB 4120, D-39016 Magdeburg, Germany

[3] Cardiff Univ, Sch Dent, Cardiff CF14 4XY, S Glam, Wales

[4] Otto von Guericke Univ, Ctr Comp, POB 4120, D-39016 Magdeburg, Germany

关键词: XXZ antiferromagnet;    Square lattice;    Easy-plane and easy-axis;    Low-energy parameters;    Spin gap;    Coupled cluster method;   

DOI  :  10.1016/j.jmmm.2016.11.043

来源: Elsevier

【 摘 要 】

We use the coupled cluster method (CCM) to study the ground-state properties and lowest-lying triplet excited state of the spin-half XXZ antiferromagnet on the square lattice. The CCM is applied to it to high orders of approximation by using an efficient computer code that has been written by us and which has been implemented to run on massively parallelized computer platforms. We are able therefore to present precise data for the basic quantities of this model over a wide range of values for the anisotropy parameter Delta in the range -1 <= Delta < infinity of interest, including both the easy-plane (-1 < Delta < 1) and easy-axis (Delta > 1) regimes, where Delta ->infinity represents the Ising limit. We present results for the ground-state energy, the sublattice magnetization, the zero-field transverse magnetic susceptibility, the spin stiffness, and the triplet spin gap. Our results provide a useful yardstick against which other approximate methods and/or experimental studies of relevant antiferromagnetic square-lattice compounds may now compare their own results. We also focus particular attention on the behaviour of these parameters for the easy-axis system in the vicinity of the isotropic Heisenberg point (Delta = 1), where the model undergoes a phase transition from a gapped state (for Delta > 1) to a gapless state (for Delta = 1), and compare our results there with those from spin-wave theory (SWT). Interestingly, the nature of the criticality at Delta = 1 for the present model with spins of spin quantum number s = 1/2 that is revealed by our CCM results seems to differ qualitatively from that predicted by SWT, which becomes exact only for its near-classical large-s counterpart.

【 授权许可】

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