The observation of the Higgs boson solidified the standard model of particle physics. However, explanations of anomalies (for example, dark matter) rely on further symmetry breaking, calling for an undiscovered axial Higgs mode¹. The Higgs mode was also seen in magnetic, superconducting and charge density wave (CDW) systems^2,3. Uncovering the vector properties of a low-energy mode is challenging, and requires going beyond typical spectroscopic or scattering techniques. Here we discover an axial Higgs mode in the CDW system RTe₃ using the interference of quantum pathways. In RTe₃ (R = La, Gd), the electronic ordering couples bands of equal or different angular momenta^4,5,6. As such, the Raman scattering tensor associated with the Higgs mode contains both symmetric and antisymmetric components, which are excited via two distinct but degenerate pathways. This leads to constructive or destructive interference of these pathways, depending on the choice of the incident and Raman-scattered light polarization. The qualitative behaviour of the Raman spectra is well captured by an appropriate tight-binding model, including an axial Higgs mode. Elucidation of the antisymmetric component is direct evidence that the Higgs mode contains an axial vector representation (that is, a pseudo-angular momentum) and hints that the CDW is unconventional. Thus, we provide a means for measuring quantum properties of collective modes without resorting to extreme experimental conditions.

希格斯玻色子的观测巩固了粒子物理学的标准模型。然而，对异常（例如暗物质）的解释依赖于进一步的对称性破坏，需要一种未被发现的轴向希格斯模式¹。希格斯模式也出现在磁性、超导和电荷密度波 (CDW) 系统^2,3中。揭示低能模式的矢量特性具有挑战性，需要超越典型的光谱或散射技术。在这里，我们利用量子路径的干涉发现了 CDW 系统 RTe _{3中的轴向希格斯模式。}在 RTe ₃ (R = La, Gd) 中，电子排序耦合相等或不同角动量的频带^4,5,6. 因此，与希格斯模式相关的拉曼散射张量包含对称和反对称分量，它们通过两个不同但简并的路径被激发。这会导致这些路径的相长或相消干涉，这取决于入射光和拉曼散射光偏振的选择。拉曼光谱的定性行为被适当的紧束缚模型很好地捕获，包括轴向希格斯模式。反对称分量的阐明是希格斯模式包含轴向矢量表示（即伪角动量）的直接证据，并暗示 CDW 是非常规的。因此，我们提供了一种无需借助极端实验条件即可测量集体模式的量子特性的方法。