Interplay of alternation and further neighbor interactions in S-1/2 spin chain Ca2CuAl4O8

Spin chains provide a testing ground for concepts in quantum magnetism. No long-range magnetic order is expected, while gapless fractional spinons excitations are predicted for spin-1/2 ions. In the case where the interactions alternate along a spin-1/2 chain the alternation confines the spinons resulting in gapped magnons. The introduction of second neighbor interactions provides another way to modify spin chains. Antiferromagnetic second neighbor interactions compete with the first neighbour interactions and exotic phases are expected such as spin-multipolar phases and nematic states in high magnetic field. Here we propose to investigate a new compound that combines alternating ferromagnetic – antiferromagnetic first neighbor interactions with stronger antiferromagnetic second neighbor interactions and is a candidate compound for nematic order in a magnetic field.

自旋链（Spin chains）为量子磁学（quantum magnetism）领域的各类概念提供了测试平台。对于自旋1/2离子（spin-1/2 ions）体系，理论预期不存在长程磁有序（long-range magnetic order），且会出现无带隙的分数自旋子激发（gapless fractional spinons excitations）。当自旋1/2链上的相互作用呈现交替分布时，这种交替相互作用会束缚自旋子，进而产生带隙磁振子（gapped magnons）。引入次近邻相互作用（second neighbor interactions）是调控自旋链的另一有效手段：反铁磁性（antiferromagnetic）次近邻相互作用会与近邻相互作用（first neighbour interactions）形成竞争，此时在强磁场（high magnetic field）环境下，有望观测到自旋多极相（spin-multipolar phases）、向列态（nematic states）等新奇物相（exotic phases）。本文拟研究一类兼具铁磁-反铁磁近邻交替相互作用与更强的反铁磁性次近邻相互作用的新型化合物（compound），该化合物是磁场下向列有序（nematic order）的候选研究对象。