  The observation of the Higgs boson solidified the standard model of particle
physics. However, explanations of anomalies (e.g. dark matter) rely on further
symmetry breaking calling for an undiscovered axial Higgs mode. In condensed
matter the Higgs was seen in magnetic, superconducting and charge density
wave(CDW) systems. Uncovering a low energy mode's vector properties is
challenging, requiring 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. As such, the
Raman scattering tensor associated to the Higgs mode contains both symmetric
and antisymmetric components, which can be 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 behavior of the Raman spectra is
well-captured by an appropriate tight-binding model including an axial Higgs
mode. The elucidation of the antisymmetric component provides direct evidence
that the Higgs mode contains an axial vector representation (i.e. a
pseudo-angular momentum) and hints the CDW in RTe3 is unconventional. Thus we
provide a means for measuring collective modes quantum properties without
resorting to extreme experimental conditions.
