标题： 非线性时间反演对称性破缺在 kagome 氦冰 HoAgGe 中 显示英文标题

标题： Nonlinear time-reversal symmetry breaking in kagome spin ice HoAgGe

摘要： 菱格自旋冰是一种有趣的自旋系统类别，由平面内伊辛自旋和铁磁相互作用组成，存在于菱格上，理论预测其具有丰富的磁性转变和激发。 特别是，不同变体的菱格自旋冰模型在从顺磁态冷却到完全有序基态的过程中可以表现出不同的对称性破缺序列。 最近的研究表明，受挫金属间化合物HoAgGe是菱格自旋冰的一个忠实固态实现。 在这里，我们使用单晶中子弥漫散射技术更准确地绘制了HoAgGe在各种温度下的自旋有序性，并意外发现有序序列似乎与之前已知的情况不同：从顺磁态开始，系统首先进入一种部分有序状态，其中存在波动的磁荷，而不是在达到完全有序状态前进入电荷有序的顺磁相。 通过最先进的蒙特卡洛模拟和使用HoAgGe中畸变菱格自旋冰的准二维模型进行的标度分析，我们阐明了一个单一的三维(3D) XY相变进入具有时间反演对称性破缺(TRS)的基态。 然而，在波动磁荷完全有序之前，3D XY相变有一个长的交叉过渡尾迹。 更有趣的是，我们发现实验和理论上，HoAgGe的时间反演对称性破缺相表现出一种异常且具有迟滞响应的现象： 尽管它们的磁化率为零，但两个时间反演伙伴被与菱格冰规则相关的非线性磁化率所区分和选择。 我们的发现不仅揭示了菱格自旋冰的一种新的对称性破缺层次结构，还展示了时间反演对称性破缺的受挫自旋系统在信息技术应用中的潜力。 显示英文摘要

摘要： Kagome spin ice is an intriguing class of spin systems constituted by in-plane Ising spins with ferromagnetic interaction residing on the kagome lattice, theoretically predicted to host a plethora of magnetic transitions and excitations. In particular, different variants of kagome spin ice models can exhibit different sequences of symmetry breaking upon cooling from the paramagnetic to the fully ordered ground state. Recently, it has been demonstrated that the frustrated intermetallic HoAgGe stands as a faithful solid-state realization of kagome spin ice. Here we use single crystal neutron diffuse scattering to map the spin ordering of HoAgGe at various temperatures more accurately and surprisingly find that the ordering sequence appears to be different from previously known scenarios: From the paramagnetic state, the system first enters a partially ordered state with fluctuating magnetic charges, in contrast to a charge-ordered paramagnetic phase before reaching the fully ordered state. Through state-of-the-art Monte Carlo simulations and scaling analyses using a quasi-2D model for the distorted Kagome spin ice in HoAgGe, we elucidate a single three-dimensional (3D) XY phase transition into the ground state with broken time-reversal symmetry (TRS). However, the 3D XY transition has a long crossover tail before the fluctuating magnetic charges fully order. More interestingly, we find both experimentally and theoretically that the TRS breaking phase of HoAgGe features an unusual, hysteretic response: In spite of their vanishing magnetization, the two time-reversal partners are distinguished and selected by a nonlinear magnetic susceptibility tied to the kagome ice rule. Our discovery not only unveils a new symmetry breaking hierarchy of kagome spin ice, but also demonstrates the potential of TRS-breaking frustrated spin systems for information technology applications.