The exploration of topological electronic phases that result from strong electronic correlations is a frontier in condensed matter physics. One class of systems that is currently emerging as a platform for such studies are so-called kagome magnets based on transition metals. Using muon spin-rotation, we explore magnetic correlations in the kagome magnet Co₃Sn_2−xIn_xS₂ as a function of In-doping, providing putative evidence for an intriguing incommensurate helimagnetic (HM) state. Our results show that, while the undoped sample exhibits an out-of-plane ferromagnetic (FM) ground state, at 5% of In-doping the system enters a state in which FM and in-plane antiferromagnetic (AFM) phases coexist. At higher doping, a HM state emerges and becomes dominant at the critical doping level of only x_cr,1 ≃ 0.3. This indicates a zero temperature first order quantum phase transition from the FM, through a mixed state, to a helical phase at x_cr,1. In addition, at x_cr,2 ≃ 1, a zero temperature second order phase transition from helical to paramagnetic phase is observed, evidencing a HM quantum critical point (QCP) in the phase diagram of the topological magnet Co₃Sn_2−xIn_xS₂. The observed diversity of interactions in the magnetic kagome lattice drives non-monotonous variations of the topological Hall response of this system.

由强电子相关性导致的拓扑电子相的探索是凝聚态物理的前沿领域。目前正在作为此类研究平台出现的一类系统是基于过渡金属的所谓的kagome磁铁。使用μ子自旋旋转，我们探索了kagome磁铁Co ₃ Sn _2−x In _x S _2中的磁相关性作为In-doping的函数，为令人着迷的不相称的电磁（HM）状态提供了推定的证据。我们的结果表明，尽管未掺杂的样品表现出面外铁磁（FM）基态，但在5％的In掺杂下，系统会进入FM和面内反铁磁（AFM）相共存的状态。在较高的掺杂下，HM状态出现，并在仅x _cr， 1≃0.3的临界掺杂水平上占主导地位 。这表明零温度一阶量子相从FM穿过混合态跃迁到x _cr，1处的螺旋相。另外，在x _cr， 2≃ 参照图1，观察到从螺旋相到顺磁相的零温度二阶相变，在拓扑磁体Co ₃ Sn _2-x In _x S ₂的相图中证明了HM量子临界点（QCP）。所观察到的磁性戈戈姆晶格中相互作用的多样性驱动了该系统的拓扑霍尔响应的非单调变化。