Hot-Phonon-Induced Distortion of Diamond Defects on Ultrafast Timescales

We investigated ultrafast defect-lattice dynamics in diamond using the Nₛ:H-C⁰ defect, an analog of bond-centered hydrogen in semiconductors. Combining synthesis, ultrafast vibrational spectroscopy, and ab initio calculations, we show that excitation of the defect's stretch mode leads to the generation of localized phonons and the formation of a hot ground state, where the interatomic potential is transiently modified. Our results reveal unexpected nonequilibrium phonon effects despite diamond's exceptionally high thermal conductivity, with implications for quantum defect engineering.