We investigated the Jahn-Teller phonon modes in ${\mathrm{LaMnO}}_3$ film grown on an orthorhombic (110)-oriented ${\mathrm{GdScO}}_3$ substrate using Raman spectroscopy, which enabled us to verify the presence of the cooperative Jahn-Teller distortion in the ultrathin limit. A characteristic $B_{1g}$ phonon mode with preserved symmetry was observed down to the two-unit-cell thickness. This finding suggests the absence of a film-thickness-driven critical transition of the cooperative Jahn-Teller distortion and the corresponding orbital order when the two-dimensional Jahn-Teller-distortion plane is designed to be parallel to the substrate by misfit strain.

• Received 15 April 2022
• Revised 22 July 2022
• Accepted 14 October 2022

DOI:https://doi.org/10.1103/PhysRevB.106.134310