Weakly Coupled S=1/2 Quantum Heisenberg Antiferromagnetic Chains in an Effective Staggered Field

正毅 押川, Masaki Oshikawa

Guang-Qiang Zhong, Shou-Shu Gong, Qing‐Rong Zheng +1 more

Masahiro Sato, Masaki Oshikawa

We study weakly coupled S = 1/2 quantum Heisenberg antiferromagnetic chains in an effective staggered field. Applying mean-field (MF) theory, spin-wave theory and chain MF (CMF) theory, we can see analytically some effects of the staggered field in this higher dimensional spin system. In particular, when the staggered field and the inter-chain interaction compete with each other, we conjecture from the MF theory that a nontrivial phase is present. The spin wave theory predicts that the behavior of the gaps induced by a staggered field is different between the competitive case and the non-competitive case. When the inter-chain interactions are weak enough, we can improve the MF phase diagram by using CMF theory and the analytical results of field theories. The ordered phase region predicted by the CMF theory is fairly smaller than one of the MF theory. Cu-benzoate, CuCl2·2DMSO (dimethylsulphoxide), BaCu2(Si1-xGex)2O7, etc., could be described by our model in enough low temperature.

Tôru Sakai

Andrei A. Zvyagin, G. A. Zvyagina

Recently several compounds were observed to reveal properties of a one-dimensional spin-$\frac{1}{2}$ antiferromagnetic Heisenberg chain with gapless low-lying spin excitations in an absence of an external magnetic field. However even a very weak external magnetic field yields an onset of a spin gap for those low-lying excitations. Usually this onset of a field-induced spin gap is related to the presence of a staggered Dzyaloshinskii-Moriya interaction, or to the staggered effective g factors of magnetic ions. Experiments on thermodynamic properties cannot distinguish between those two origins for the spin-gap formation. Here we propose the setup for an experiment, in which one can clearly distinguish between the staggered Dzyaloshinskii-Moriya coupling and staggered external magnetic field: an electronic paramagnetic resonance in the parallel pumping geometry. The characteristics of the system under conditions of such an experiment, i.e., the renormalization of the homogeneous and staggered magnetizations, power of the microwave magnetic field, absorbed by the system, are calculated. Several important features of the solution are discussed.

Z. Song