Recent improvements in the energy resolution of resonant inelastic x-ray scattering experiments (RIXS) at the Cu-L3 edge have enabled the study of lattice, spin, and charge excitations. Here, we report on the detection of a low intensity signal at 140meV, twice the energy of the bond-stretching (BS) phonon mode, in the cuprate superconductor Bi2Sr2CaCu2O8+x (Bi-2212). Ultra-high resolution polarimetric RIXS measurements allow us to resolve the outgoing polarization of the signal and identify this feature as a two-phonon excitation. Further, we study the connection between the two-phonon mode and the BS one-phonon mode by constructing a joint density of states toy model that reproduces the key features of the data.
@article{arxiv.2309.15989,
title = {Detection of a two-phonon mode in a cuprate superconductor via polarimetric RIXS},
author = {Kirsty Scott and Elliot Kisiel and Flora Yakhou and Stefano Agrestini and Mirian Garcia-Fernandez and Kurt Kummer and Jaewon Choi and Ruidan Zhong and John A. Schneeloch and Genda D. Gu and Ke-Jin Zhou and Nicholas B. Brookes and Alexander F. Kemper and Matteo Minola and Fabio Boschini and Alex Frano and Adrian Gozar and Eduardo H. da Silva Neto},
journal= {arXiv preprint arXiv:2309.15989},
year = {2024}
}