We investigate ultrafast dynamics from photoinduced reflectivity of ${\mathrm{Sr}}_2{\mathrm{RhO}}_4$ by using femtosecond near-infrared pulses. We observe a clear temperature dependent anomaly in its electronic dynamics which slows down below $T_{\mathrm{S}}\sim 160$ K. In addition, coherent oscillations of the 5.3 THz $A_{1g}$ phonon exhibit a ${90}^{\circ }$ shift in its initial phase across $T_{\mathrm{S}}$, indicating a structural change in octahedral rotation distortions. We propose that octahedral structure in ${\mathrm{Sr}}_2{\mathrm{RhO}}_4$ evolves around $T_{\mathrm{S}}$, and it can influence the nonequilibrium dynamics of photo-induced carriers as well as realtime phonon responses.

• Received 12 August 2019
• Revised 2 December 2019

DOI:https://doi.org/10.1103/PhysRevB.100.235139