Correlated motion of particle-hole excitations across the renormalized spin-orbit gap in $\rm Sr_2 Ir O_4$

Abstract

The high-energy collective modes of particle-hole excitations across the spin-orbit gap in Sr 2 IrO 4 are investigated using the transformed Coulomb interaction terms in the pseudo-spin-orbital basis constituted by the J = 1/2 and 3/2 states arising from spin-orbit coupling. With appropriate interaction strengths and renormalized spin-orbit gap, these collective modes yield two well-defined propagating spin-orbit exciton modes, with energy scale and dispersion in excellent agreement with resonant inelastic X-ray scattering (RIXS) measurements.