Unraveling spin and charge dynamics in two-leg spin ladders using resonant inelastic x-ray scattering

Resonant inelastic x-ray scattering (RIXS) has become an important tool to study the spin and charge excitations in materials. We investigate the RIXS spectra of undoped and doped antiferromagnetic spin-ladder cuprate in both the non-spin conserving (NSC) and spin-conserving (SC) channels at the Cu L₃ -edge. The spectra are rich and host many exotic excitations. In the undoped NSC-channel, we identify one-triplon, triplet two-triplon excitations in the strong rung coupling limit and confined spinons in the weak rung coupling limit. In the doped NSC-channel, we identify a new dispersive quasiparticle-like spectral features composed of bound 'charge and spin-1/2' in strong rung coupling limit in addition to the excitations branches already present in the undoped case. The NSC-channel can be well described by S(q, ω). On the other hand, SC-channel is unique to RIXS and reveals new features. In the undoped SC channel, we identify singlet two-triplon for the strong rung coupling and confined spinons for the weak rung coupling. In the doped SC-channel, RIXS probes the charge excitations instead of spin-excitations, and we identify gapless and gapped charge excitations in the spectra.