Spinel oxides are well-known functional materials but rarely show superconductivity. Recently, emergent superconductivity was discovered in ${\mathrm{MgTi}}_2{\mathrm{O}}_4$, which is attributed to the increase of electron doping and the suppression of orbital order. Here, we utilized Ti $L$-edge resonant inelastic x-ray scattering to study the orbital excitations in superconducting (SC) and insulating ${\mathrm{MgTi}}_2{\mathrm{O}}_4$ films. We find that the spectral weight of orbital excitations is enhanced and the energy of $t_{2g}$ intraband excitation is softened in the SC film compared to the insulating one, suggesting higher electron doping and a suppressed orbital order gap in the SC sample. These observations were further supported by our multiplet calculations using the minimal two-site model. Our results provide spectroscopic evidence for the competition between orbital order and superconductivity in ${\mathrm{MgTi}}_2{\mathrm{O}}_4$ and shed light on searching for novel superconductors in spinel oxides.

• Received 17 January 2023
• Revised 9 March 2023
• Accepted 13 March 2023

DOI:https://doi.org/10.1103/PhysRevB.107.L121108