Investigating quantum geometry in a two-gap superconductor using RIXS

Despite falling within the conventional paradigm of superconductivity, MgB₂ exhibits a respectable transition temperature (T_c) of 39 K, traditionally attributed to a strong, but orthodox electron-phonon interaction. However, recent theoretical work has proposed that MgB₂’s electronic band structure may host a large geometric contribution to the electron-phonon coupling, arising from its topological properties. To explore these contributions, we conducted a resonant inelastic X-ray scattering (RIXS) study at the B K-edge, aiming to site-selectively probe the electronic structure and excitations in MgB₂. Our RIXS measurements reveal a feature that disperses in momentum space with a significant slope, consistent with either interband or intraband transitions. This momentum-dependent feature may offer new insights into the electronic structure and coupling mechanisms within MgB₂, shedding light on the possible interplay between its band topology and superconducting properties. These results provide a pathway for evaluating the role of unconventional interactions in MgB₂ and similar materials.