Novel routes to magnetic frustration

我们在过去40年中看到的技术革命是由世纪初发展起来的量子力学推动的。量子力学最初是基于单个原子和非相互作用粒子（如自由电子）的性质。对它的原理有了深刻的理解，我们就有了半导体晶体管和铁磁体存储器。然而，我们开始意识到，许多粒子之间的强相互作用会导致新的涌现现象，以及新的相。对这些相的探索是推动人们对受抑磁性感兴趣的原因。这又回到了在三角形上放置三个具有反铁磁相互作用的自旋的几何问题。最近的邻居之间的相互作用有利于两个相邻自旋中的任何一个之间的反平行对齐，这是一个不可能同时满足三个自旋的条件。量子力学涨落和几何约束阻止有序的系统被称为量子自旋液体（QSL）。这些基态具有真正的奇异激发，这在任何其他系统中都无法研究。例如，QSL中的激发可以是费米子的，这使得它们与有序磁态中的激发完全不同，有序磁态中的激发总是玻色子。此外，QSL中的自旋在长距离上量子力学纠缠，导致拓扑波函数，这使它们具有量子计算应用所需的特性。虽然在过去只能在理论模型中研究QSL，但由于发现了一些候选材料，我们目前正处于突破的风口浪尖。这项资助将使我们能够使用多种晶体化学方法来合成新型的受挫折磁铁。我们计划研究的材料是基于三角形图案上的强相互作用自旋，该图案在三维（Ce 2 Zr 2 O 7）或一维（BaRE 2 O 4）中重复自身，并且在3D中为自旋1/2（PbCuTe 2 O 6）的罕见情况。一旦合成，我们将首先通过比热和磁化测量来表征这些材料的热力学性质，以测试是否存在有序。随后将进行详细的单晶中子衍射实验。中子散射不仅可以让我们证明有序的缺失，而且它是探测QSL的直接方法，因为它测量了磁结构因子。在所提出的材料中找到QSL基态将对受抑磁性领域产生真正的变革性影响。它将给我们一个实验室，在那里我们可以探索迷人的准粒子的新物理学，这是详细理解的第一步。我们相信，这样的理解对于在量子计算中开发基于QSL的应用程序的路径至关重要，其中QSL可用于强大的纠错方案。

The technological revolution we have seen unfolding over the last 40 years was fueled by quantum mechanics, which was developed in the early 20th century. Quantum mechanics was first based on the properties of individual atoms, and non-interacting particles, such as free electrons. A firm understanding of its principles gave us semiconductors for transistors, and ferromagnets for storage. However, we came to realize that strong interactions between many particles lead to new emergent phenomena, as well as novel phases.******The search for such phases is what is driving the interest in frustrated magnetism. It goes back to the geometric problem of placing three spins with antiferromagnetic interactions on a triangle. The interaction between nearest neighbors favors an anti-parallel alignment between any of two neighboring spins, which is a condition that is impossible to fulfill simultaneously for the three spins.******Systems where quantum mechanical fluctuations, and geometrical constraints prevent order, are called quantum spin liquids (QSL). These ground states have truly exotic excitations, which cannot be studied in any other systems. For example, excitations in a QSL can be fermionic, which makes them completely different from the excitations in an ordered magnetic state, which are always bosonic. Furthermore, the spins in a QSL are quantum mechanically entangled over long distances leading to topological wave functions which gives them properties which are desired for applications in quantum computing.******While in the past it has only been possible to study QSL in theoretical models, we are currently at the cusp of a breakthrough due to the discovery of a number of candidate materials. This grant will allow us to use multiple crystal chemistry methods to synthesize new classes of frustrated magnets. The materials we are planning to study are based on strongly interacting spins on a triangular motif which repeats itself in three dimensions (Ce2Zr2O7), or one dimension (BaRE2O4), and in 3D for the rare case of spin 1/2 (PbCuTe2O6). Once synthesized, we will first characterize the thermodynamic properties of these materials by specific heat and magnetization measurements to test for the absence of order. This will be followed by detailed neutron diffraction experiments on single crystals. Neutron scattering will not only allow us to show the absence of order, but it is the direct way to probe a QSL, as it measures the magnetic structure factor.******Finding a QSL ground state in one of the proposed materials would have a truly transformative impact on the field of frustrated magnetism. It would give us a laboratory in which we can probe novel physics of fascinating quasiparticles, which is the first step to a detailed understanding. We believe that such an understanding is critical for the path to develop applications based on QSL's in quantum computing, where QSL's could be used for robust error corrections schemes.