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) systems2,3. 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 momenta4,5,6. 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.
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The datasets generated and/or analysed during the current study are available from the OSF storage https://osf.io/87bxy/.
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We thank L. Benfatto and A. Chubukov for useful discussions about the CDW Raman response. Y.W. is grateful for the support of the Office of Naval Research under award number N00014-20-1-2308. K.S.B. and L.M.S. acknowledge joint support by the Air Force office of Scientific Research under award number FA9550-20-1-0246. The work of G.M. was supported by the National Science Foundation via award DMR-2003343. M.M.H. acknowledges the primary support of the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences under award number DE-SC0018675. L.M.S. acknowledges support from the Gordon and Betty Moore Foundation (EPiQS Synthesis Award) through grant GBMF9064, the David and Lucile Packard Foundation and the Sloan Foundation. J.J.C. and J.L.H. gratefully acknowledge support from the Gordon and Betty Moore Foundation (EPiQS Synthesis Award). Y.-C.W. and J.Y. are supported by the National Science Foundation under award number DMR-2004474. Work by D.X. is supported by DOE award number DE-SC0012509. I.P. and P.N. are primarily supported by the Quantum Science Center (QSC), a National Quantum Information Science Research Center of the US DOE. Theory by I.P. and P.N. is supported by the QSC. I.P. was partially supported by the Swiss National Science Foundation (SNSF) under project ID P2EZP2_199848. P.N. is a Moore Inventor Fellow and gratefully acknowledges partial support through grant GBMF8048 from the Gordon and Betty Moore Foundation.
The authors declare no competing interests.
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Wang, Y., Petrides, I., McNamara, G. et al. Axial Higgs mode detected by quantum pathway interference in RTe3. Nature 606, 896–901 (2022). https://doi.org/10.1038/s41586-022-04746-6