Improper Ferroelectricity at the Monolayer Limit
Abstract
Ultrathin ferroelectric films with out-of-plane polarization and high Curie temperatures are key to miniaturizing electronic devices. Most ferroelectrics employed in devices are proper ferroelectrics, where spontaneous polarization is the primary order parameter. Unfortunately, the Curie temperature of proper ferroelectrics is drastically reduced as the ferroelectric becomes thin; nearly all proper ferroelectrics need to be thicker than several unit cells. The absence of an ultrathin limit has been predicted, but not verified for improper ferroelectrics. These are ferroelectrics where the polarization emerges secondary to the primary order parameter, such as a structural distortion. Here we report improper ferroelectricity with an undiminished Curie temperature in a 0.75-unit-cell-thick hexagonal LuFeO3 (h-LuFeO3) film grown on a SrCo2Ru4O11 bottom electrode with an atomically engineered monolayer bridging layer. Our results demonstrate the absence of a critical thickness for improper ferroelectricity and provide a methodology for creating ultrathin improper ferroelectrics by stabilizing their primary order parameters.
Cite
@article{arxiv.2503.06214,
title = {Improper Ferroelectricity at the Monolayer Limit},
author = {Yilin Evan Li and Harikrishnan KP and Haidong Lu and Rachel A. Steinhardt and Megan E. Holtz and Mario Brützam and Matthew M. Dykes and Elke Arenholz and Sankalpa Hazra and Adriana LaVopa and Xiaoxi Huang and Wenwen Zhao and Piush Behera and Maya Ramesh and Evan Krysko and Venkatraman Gopalan and Ramamoorthy Ramesh and Craig J. Fennie and Robert J. Cava and Christo Guguschev and Alexei Gruverman and David A. Muller and Darrell G. Schlom},
journal= {arXiv preprint arXiv:2503.06214},
year = {2025}
}