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）是检验量子磁学（quantum magnetism）相关概念的理想实验平台。理论预言其不具备长程磁序（long-range magnetic order），且自旋1/2离子体系中会出现无带隙的分数化自旋子（spinons）激发。当自旋1/2链上的相互作用呈交替分布时，这种交替相互作用会束缚自旋子，进而产生有带隙的磁振子（magnons）。引入次近邻相互作用是另一种调控自旋链的有效途径：反铁磁次近邻相互作用会与近邻相互作用形成竞争，此时有望在高磁场环境下出现多种新奇物相，例如自旋多极相与向列态。本文拟研究一种新型化合物，该化合物兼具交替的铁磁-反铁磁近邻相互作用与更强的反铁磁次近邻相互作用，是磁场中向列序的潜在候选化合物。