标题： 金刚石装饰晶格上铁-反铁磁海森堡模型的宏观基态简并性 显示英文标题

标题： Macroscopic ground state degeneracy of the ferro-antiferromagnetic Heisenberg model on diamond-decorated lattices

摘要： 我们研究了自旋-1/2海森堡模型在金刚石装饰晶格上具有竞争性铁磁和反铁磁相互作用的情况。 通过调整交换相互作用到铁磁相的边界，我们分析了两种类型的金刚石单元模型：扭曲的和理想的金刚石。 在扭曲的金刚石模型中，磁子谱中的平带表明局域态被限制在晶格的小区域（“捕获单元”）内。 值得注意的是，对于正方形和立方晶格，这些捕获单元分别可以容纳多达五个和七个局域态，从而导致宏观基态简并性和残余熵的高值。 计算基态简并度的问题简化为非相互作用自旋的问题，其自旋值等于捕获单元中局域磁子数量的一半。 相比之下，理想的金刚石模型具有由随机分布的孤立金刚石对角线双线态组成的基态，这些双线态浸没在铁磁背景中。 在这里计算基态简并度映射到了二维和三维晶格上的渗流问题。 我们的分析表明，理想的金刚石模型比其扭曲的对应物具有更大的基态简并度。 这些发现表明合成金刚石装饰型化合物在低温冷却应用方面具有巨大潜力。 显示英文摘要

摘要： We investigate the spin-1/2 Heisenberg model with competing ferromagnetic and antiferromagnetic interactions on diamond-decorated lattices. Tuning the exchange interactions to the boundary of the ferromagnetic phase, we analyze the models with two types of diamond units: distorted and ideal diamonds. In the distorted diamond model, flat bands in the magnon spectra indicate the localized states confined to small regions (`trapping cells') of the lattice. Remarkably, these trapping cells can host up to five and seven localized states for square and cubic lattices, respectively, leading to the macroscopic ground state degeneracy and high value of residual entropy. The problem of calculating ground state degeneracy reduces to that of non-interacting spins, whose spin value equal to half the number of localized magnons in the trapping cell. In contrast, ideal diamond models feature ground states composed of randomly distributed isolated diamond diagonal singlets immersed in a ferromagnetic background. Counting the ground state degeneracies here maps onto the percolation problem in 2D and 3D lattices. Our analysis shows that ideal diamond models possess even greater ground state degeneracy than their distorted counterparts. These findings suggest that synthesizing diamond-decorated-type compounds holds great promise for low-temperature cooling applications.