High-resolution RIXS investigation of a cascade of excitations in a 5d1 double perovskite Ba2MgReO6

This proposal concerns the study of local excitations in Ba2MgReO6, a 5d1 system shown recently to display multipolar order, with strong entanglement between spin, orbit and vibronic degrees of freedom. The local ReO6 environment is highly-symmetric, recently shown to be distorted due to the dynamical Jahn-Teller effect. Our previous RIXS data revealed two main d-d excitations, the splitting of the jeff=3/2 quartet into two doublets and the SOC-induced gap. Each d-d excitation develops a high-energy tail, which has been described using a set of equidistant modes, but the low resolution did not allow to properly characterize their energies and the number of those additional modes. The current experiment aims to address this problem by utilising high-resolution RIXS beamline at ID32. We plan to measure RIXS at the O K-edge of Ba2MgReO6, with the desired resolution of 20meV fully achievable on this instrument.