Spin Dynamics and Resonant Inelastic X-ray Scattering in Chromium with Commensurate Spin-Density Wave Order

After the discovery of iron-pnictide superconductors, the spin dynamics of itinerant antiferromagnetic systems with multi-orbital has attracted much attention. In order to elucidate such spin dynamics, we focus on a similar system, chromium, which is known to show a spin density wave (SDW), and theoretically investigate dynamical spin susceptibilities and $L_3$-edge resonant inelastic X-ray scattering (RIXS) spectra [1]. We use multi-band Hubbard model composed of $3d$ and $4s$ orbitals. After the SDW mean-field approximation, we obtain the dynamical spin susceptibilities and RIXS spectra by employing random phase approximation. In our calculation, we assume the perfect commensurate SDW state. We find a collective spin-wave excitation undamped up to $\sim 0.6$~eV. Above the energy, excitation overlaps individual particle-hole excitations as expected. In RIXS spectra, particle-hole excitations with various orbital channels show a large spectral weight, masking the spectra of the spin collective mode. However, it may be possible to detect the spin-wave excitation in RIXS experiments in the future if resolution is high enough. [1] K. Sugimoto, Z. Li, E. Kaneshita, K. Tsutsui, and T. Tohyama, arXiv:1211.1598