Novel routes to magnetic frustration

我们在过去40年里看到的技术革命是由20世纪初发展起来的量子力学推动的。量子力学首先是基于单个原子和不相互作用的粒子的性质，如自由电子。对其原理的深刻理解使我们可以用半导体做晶体管，用铁磁体做存储材料。然而，我们逐渐意识到，许多粒子之间的强烈相互作用导致了新的出现现象，以及新的相。*对这些相的探索推动了人们对受挫磁性的兴趣。它回到了在一个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。近邻之间的相互作用有利于两个相邻自旋之间的反平行排列，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碍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，这是在任何其他系统中都无法研究的。例如，QSL中的激发可以是费米子的，这使得它们与有序磁状态下的激发完全不同，有序磁状态下的激发总是玻色子的。此外，QSL中的自旋在很长的距离内被量子力学纠缠，从而产生了拓扑波函数，这使得它们具有在量子计算中应用所需的性质。尽管过去只能通过理论模型来研究QSL，但由于许多候选材料的发现，我们目前正处于突破的边缘。这笔赠款将允许我们使用多种晶体化学方法来合成新类别的受挫磁铁。我们计划研究的材料是基于一个三角形基序上的强相互作用自旋，这个三角形基序在三维(Ce2Zr2O7)或一维(BaRE2O4)上重复自己，而在3D中，对于罕见的自旋1/2(PbCuTe2O6)。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，以测试是否没有有序。随后将对单晶进行详细的中子衍射实验。中子散射不仅可以让我们看到无序现象，而且是探测类星体的直接方法，因为它测量了磁结构因子。*在一种被提议的材料中发现类星体基态将对受挫磁性领域产生真正的变革性影响。它将为我们提供一个实验室，在那里我们可以探索令人着迷的准粒子的新物理，这是详细理解的第一步。我们认为，这样的理解对于在量子计算中开发基于QSL的应用程序至关重要，在量子计算中，QSL可以用于健壮的纠错方案。

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.