The precise crystal structure of La3Ni2O7 in its high-pressure superconducting state has been a subject of intense debate, with proposed models including both orthorhombic and tetragonal symmetries. Using high-pressure Raman spectroscopy combined with frst-principles calculations, we unravel the structural evolution of La3Ni2O7 under pressure up to 32.7 GPa. We identify a clear structural transition sequence: from the orthorhombic Amam phase to a mixed Amam+Fmmm phase at 4 GPa, followed by a complete transition to the tetragonal I4/mmm phase at 14.5 GPa, which is signaled by a pronounced phonon renormalization. The emergence of bulk superconductivity is found to coincide precisely with this transition to the I4/mmm phase. Our results de nitively establish the tetragonal I4/mmm structure as the host of superconductivity in La3Ni2O7, resolving a central controversy and providing a critical foundation for understanding the superconducting mechanism in nickelates.
@article{arxiv.2511.15265,
title = {Identifying the structure of La3Ni2O7 in the pressurized superconducting state},
author = {Hengyuan Zhang and Jielong Zhang and Mengwu Huo and Junfeng Chen and Deyuan Hu and Dao-Xin Yao and Hualei Sun and Kun Cao and Meng Wang},
journal= {arXiv preprint arXiv:2511.15265},
year = {2025}
}