Spin dynamics and spin freezing at ferromagnetic quantum phase transitions

越来越多的实验和理论研究表明，巡回电子铁磁体的量子临界性一般不存在于实际材料中。这就提出了这样一个问题：是什么机制先发制人，才能预防铁磁量子临界性。在最简单的情况下，单粒子态密度或某些多体相互作用驱动量子相变的一级。进一步的可能性包括出现有序相，例如超导或部分电子有序，例如向列相电子相。最后，由微弱的残余相互作用驱动的长程调制和电子相分离的出现是可以预料的。我们建议使用中子去极化射线照相术和中子去极化层析照相术在过渡金属和稀土化合物中寻找铁磁量子临界附近的电子相分离；这些是我们在第一个资助期内开发的新的中子散射技术。我们的研究将得到常规的非弹性中子散射研究和块体性质的全面测量的补充。

An increasing number of experimental and theoretical studies suggest that quantum criticality of itinerant-electron ferromagnets, quite generally, does not exist in real materials. This raises the question what mechanisms pre-empt ferromagnetic quantum criticality. In the simplest scenario the single-particle density of states or certain many body interactions drive the quantum phase transition first order. Further possibilities include the emergence of ordered phases such as superconductivity or partial electronic order, e.g., nematic electronic phases. Finally, the emergence of long-range modulations and electronic phase separations may be expected that are driven by weak residual interactions. We propose to search for electronic phase separations near ferromagnetic quantum criticality in a wide range of transition metal and rare earth compounds using neutron depolarization radiography and neutron depolarization tomography; these are new neutron scattering techniques we developed during the first funding period. Our studies will be complemented by conventional inelastic neutron scattering studies and comprehensive measurements of the bulk properties.