Thermodynamics of frustrated spin lattices with flat bands

平带受挫自旋晶格的热力学

• 批准号: 449703145
• 负责人: Professor Dr. Johannes Richter
• 金额: --
• 依托单位: Arbeitsgruppe Theorie der Kondensierten Materie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/449703145?language=en
• 关键词: Thermodynamics; frustrated; spin; lattices; flat

The central goal of our project is the evaluation and subsequentanalysis of thermodynamic properties of frustrated quantum spin lattices for as big lattice sizes as possible. We are convinced that this is a unique opportunity since we could assemble the neccessary prerequisites in our team: long experience with frustrated quantum spin lattices, long experience with the finite-temperature Lanczos method (FTLM,) and last but not least direct access to the code spinpack. This code enables us to use the new supercomputer supermuc-ng at the Leibniz Supercomputing Center (LRZ) Garching with up to the Maximum number of nodes, 3076, i.e. 147,648 cores. We belong to those users who were given access prior to public use in order to test the machine. In particular, we want to investigate thermodynamic properties of the kagome lattice Heisenberg antiferromagnet (KHAF) for sizes N=45 and N=48 at the 1/3rd magnetization plateau in order to elucidate the phenomenon of asymmetric melting. Temperature and field dependent magnetization as well as the density of states will be studied. For lattice sizes of up to N=81 we want to study magnon crystallization on the KHAF, for which first investigations below the saturation field, i.e. at the 7/9 magnetization plateau, strongly point at a phase transition of the sameuniversality class as the two-dimensional 3-states Potts model. The magnon condensation suggested by a Japanese team for other magnetization plateaus, shall be investigated as well. We are convinced that they are of different origin. Our investigations shall be completed by similar studies for related frustrated spin systems that also possess flat bands, in particular the square kagome lattice and the planar pyrochlore lattice. Especially the square kagome lattice turned out to be an urgent problem since this structure could be synthesized quite recently and first experiments were published. During the last third of the project duration we would like to move away from a Heisenberg model towards XXZ couplings as well as next-nearest neighbor couplings in order to tune the frustration of the system as well as to deform the flat bands. This not only addresses realistic compounds, but should also help to understand the impact of specific frustration effects on e.g. magnetocaloric properties. Another issue along this line is the investigation how the spin quantum number influences the addressed properties.Besides comparing the various lattices, the J1-J2 square lattice throughout theproject will serve as reference system with tunable frustration. In addition, thermodynamic functions will be compared with an interpolation method that rests on high-temperature series expansions combined with a so-called entropy method.

本课题的主要目标是在尽可能大的晶格尺寸下对受抑量子自旋晶格的热力学性质进行评估和分析。我们相信这是一个独特的机会，因为我们可以在我们的团队中组装必要的先决条件：与挫折量子自旋晶格的长期经验，有限温度Lanczos方法（FTLM）的长期经验，最后但并非最不重要的是直接访问代码spinpack。此代码使我们能够使用Leibniz超级计算中心（LRZ）Garching的新超级计算机supermuc-ng，最大节点数为3076，即147，648个核心。我们属于那些在公开使用之前获得访问权限以测试机器的用户。特别是，我们要调查的kagome晶格海森堡反铁磁体（KHAF）的尺寸为N=45和N=48在1/3磁化平台的热力学性质，以阐明不对称熔化的现象。温度和磁场依赖的磁化强度以及态密度将被研究。对于晶格尺寸高达N=81，我们要研究磁振子结晶的KHAF，第一次调查低于饱和场，即在7/9磁化平台，强烈点在same普适性类的相变作为二维3-状态Potts模型。由日本研究小组提出的其他磁化平台的磁振子凝聚，也将进行调查。我们相信它们是不同的起源。我们的调查将完成类似的研究相关的挫折自旋系统，也具有平坦的带，特别是方形kagome晶格和平面烧绿石晶格。特别是方形kagome晶格原来是一个紧迫的问题，因为这种结构可以合成相当最近和第一个实验发表。在项目持续时间的最后三分之一，我们想从海森堡模型转向XXZ耦合以及次近邻耦合，以调整系统的挫折以及使平带变形。这不仅解决了现实的化合物，但也应该有助于了解特定的挫折效应的影响，例如磁热性能。沿着这条路线的另一个问题是研究自旋量子数如何影响所寻址的性质。除了比较各种晶格之外，整个项目中的J1-J2正方形晶格将作为具有可调阻挫的参考系统。此外，热力学函数将与插值方法进行比较，该方法基于高温级数展开与所谓的熵方法相结合。