Shin Soohyeon, Ramires Aline, Pomjakushin Vladimir, Plokhikh Igor, Pomjakushina Ekaterina
Laboratory for Multiscale Materials Experiments (LMX), PSI Center for Neutron and Muon Sciences, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
Laboratory for Theoretical and Computational Physics (LTC), PSI Center for Scientific Computing, Theory and Data, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
Nat Commun. 2024 Sep 28;15(1):8423. doi: 10.1038/s41467-024-52720-9.
Quantum critical points (QCPs), zero-temperature phase transitions, are windows to fundamental quantum-mechanical phenomena associated with universal behaviour. Magnetic QCPs have been extensively investigated in the vicinity of antiferromagnetic order. However, QCPs are rare in metallic ferromagnets due to the coupling of the order parameter to electronic soft modes. Recently, antisymmetric spin-orbit coupling in noncentrosymmetric systems was suggested to protect ferromagnetic QCPs. Nonetheless, multiple centrosymmetric materials host FM QCPs, suggesting a more general mechanism behind their protection. In this context, CeSi, a dense Kondo lattice crystallising in a centrosymmetric structure, exhibits ferromagnetic order when Si is replaced with Ag. We report that the Ag-substitution to CeSi linearly suppresses the ferromagnetic order towards a QCP, accompanied by concurrent strange-metal behaviour. Herein, we suggest that, despite the centrosymmetric structure, spin-orbit coupling arising from the local noncentrosymmetric structure, in combination with nonsymmorphic symmetry, can protect ferromagnetic QCPs. Our findings offer a general guideline for discovering new ferromagnetic QCPs and highlight one new family of materials within which the interplay of topology and quantum phase transitions can be investigated in the context of strongly correlated systems.
量子临界点（QCPs），即零温度相变，是通向与普遍行为相关的基本量子力学现象的窗口。磁性量子临界点已在反铁磁序附近得到广泛研究。然而，由于序参量与电子软模的耦合，量子临界点在金属铁磁体中很少见。最近，有人提出非中心对称系统中的反对称自旋轨道耦合可以保护铁磁量子临界点。尽管如此，多种中心对称材料中存在铁磁量子临界点，这表明其背后存在更普遍的机制。在此背景下，CeSi是一种以中心对称结构结晶的致密近藤晶格，当用Ag取代Si时会表现出铁磁序。我们报道，用Ag取代CeSi中的Si会线性地将铁磁序抑制到一个量子临界点，同时伴随着奇异金属行为。在此，我们认为，尽管具有中心对称结构，但由局部非中心对称结构产生的自旋轨道耦合与非简单空间群对称性相结合，可以保护铁磁量子临界点。我们的发现为发现新的铁磁量子临界点提供了一个通用指南，并突出了一类新的材料，在这类材料中，可以在强关联系统的背景下研究拓扑结构与量子相变之间的相互作用。
