Axial Higgs Mode Detected by Quantum Pathway Interference in RTe3

TL;DR

This paper reports the discovery of an axial Higgs mode in the charge density wave system RTe3 using quantum pathway interference in Raman scattering, revealing its vector properties and unconventional nature.

Contribution

It introduces a novel method to detect the axial Higgs mode via interference of quantum pathways in Raman spectroscopy, demonstrating its vector character in RTe3.

Findings

Axial Higgs mode observed in RTe3 using interference effects.

Raman tensor contains symmetric and antisymmetric components.

The Higgs mode exhibits an axial vector (pseudo-angular momentum) property.

Abstract

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.