Probing signatures of spin fractionalization in Quantum Spin Liquid phases via vibrational Raman spectroscopy*

We study the magnetoelastic coupling in Quantum Spin Liquids(QSL) to explore possible signatures of spin fractionalization. Two concrete realizations are studied: Pr₂Zr₂O₇ and Cu₂IrO₃, candidates for non-Kramers U(1) and second-generation Kitaev QSL respectively. Renormalization of phonon linewidth and frequency due to the couplings are calculated by studying scattering channels that open up in the low-temperature QSL phase via fractionalization. In Cu₂IrO₃, broadening of linewidth shows fermionic temperature evolution as a result of effective Majorana-phonon interaction and its frequency dependence is sensitive to the two-Majorana density of states(DOS). In the case of non-Kramers Pr₂Zr₂O₇, a linear spin-phonon coupling is derived which is expected to be dominant than the familiar quadratic coupling. Phonon linewidth is calculated for different scattering channels due to magnetic monopoles, electric charges and photons. While its temperature dependence shows the bosonic behavior of the excitations, the frequency dependence follows their two-particle DOS. Due to the natural separation of the energy scale of three excitations, their spectroscopic signature occurs at different frequency regimes which might be important to characterize the fractionalized excitations experimentally.