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）是验证量子磁学（quantum magnetism）各类理论概念的经典实验平台。理论预言，由自旋1/2离子构成的自旋链不会出现长程磁序，且存在无带隙分数自旋子激发（gapless fractional spinons excitations）。若自旋1/2链内的相互作用存在交替，则这种交替作用会束缚自旋子，进而产生带隙磁振子（gapped magnons）激发。引入次近邻相互作用是调控自旋链的另一有效手段：反铁磁次近邻相互作用会与近邻相互作用产生竞争，此时在强磁场环境下有望涌现自旋多极相（spin-multipolar phases）与向列态（nematic states）等诸多新奇物相。本文拟研究一种兼具交替铁磁-反铁磁近邻相互作用与更强反铁磁次近邻相互作用的新型化合物，该化合物可作为磁场下向列序（nematic order）的候选研究体系。