Non-linear temperature dependent phononic response of epitaxial lanthanum nickelate thin film

From the temperature dependent Raman spectroscopy study (80 K–300 K) on epitaxial thin film of lanthanum nickelate (LNO), we find that the characteristics Raman active phonon modes (A1g and Eg) of LNO soften with an increase in the temperature. The extent of softening is greater for the A1g mode owing to substrate induced strain. In addition, temperature dependent Raman shifts presented with some non-linearities. Our analysis suggests that these non linearities arise due to an anharmonic contribution to the Raman shifts. We find that for A1g mode, four-phonon anharmonic process contributed most to the temperature dependent Raman shifts, while the contributions from three-phonon, strain and thermal expansion effect found to be relatively small. However, for Eg mode, the shift originated mainly from the thermal expansion effect.

This project has received funding from EU-H2020 research and innovation programme under grant agreement No. 654360 within NFFA- Europe transnational access activity. We also thank UGC-DAE Consortium for Scientific Research, Indore for providing Temperature dependent Raman measurements facility. Ms. Sunidhi expresses her thanks to UGC, New Delhi for providing fellowship for research work. Florencio Sánchez acknowledges financial support from the Spanish Ministry of Science and Innovation, through the MAT2017-85232-R (AEI / FEDER, EU) and SEV-2015-0496 projects, and from Generalitat de Catalunya (2017 SGR 1377).