We use polarization resolved Raman spectroscopy to demonstrate that for a 3D giant Rashba system the bulk plasmon collective mode can directly couple to the Raman response even in the long wavelength q→0 limit. Although conventional theory predicts the plasmon spectral weight to be suppressed as the square of its quasi-momentum and thus negligibly weak in the Raman spectra, we observe a sharp in-gap plasmon mode in the Raman spectrum of BiTeI below the Rashba continuum. This coupling, in a polar system with spin-orbit coupling, occurs without assistance from phonons when the incoming photon excitation is resonant with Rashba-split intermediate states. We discuss the distinctive features of BiTeI's giant Rashba system band structure that enable the direct observation of plasmon in Raman scattering.
@article{arxiv.2310.04394,
title = {Spin-Mediated Direct Photon Scattering by Plasmons in BiTeI},
author = {A. C. Lee and S. Sarkar and K. Du and H. -H. Kung and C. J. Won and K. Wang and S. -W. Cheong and S. Maiti and G. Blumberg},
journal= {arXiv preprint arXiv:2310.04394},
year = {2024}
}