For decades, ferroelectric materials with complex layered structures were thought too difficult to grow with the quality needed for device applications. Among them is the long-overlooked Carpy–Galy family, named after CNRS researchers Alain Carpy and Jean Galy, who first synthesized and characterized these compounds in 1972. Comprising perovskite-like layers interleaved with additional oxygen sheets, these materials were primarily investigated only as bulk crystals.

In our recent work published in Advanced Materials, we revisited this overlooked family of ferroelectrics and showed that a refined epitaxial approach using pulsed laser deposition with real-time growth monitoring, can stabilize high-quality, single-crystalline La₂Ti₂O₇ films.

Remarkably, the Carpy-Galy films maintain ferroelectricity down to a single unit cell (1.3 nm thick), unlike conventional perovskite ferroelectrics that usually need at least 2 nm. Moreover, our La₂Ti₂O₇ films exhibit a polarization nearly four times higher than ever previously reported. This boost can be attributed to epitaxy, which not only stabilizes the structure but also enhances its intrinsic ferroelectric properties. By resolving atomic displacements with scanning transmission electron microscopy and backing our findings with density-functional theory, we have unlocked the potential of these materials for next-generation electronic devices.

This research was led at the Laboratoire Albert Fert (Elzbieta Gradauskaite, Anouk S. Goossens, Lucía Iglesias, Manuel Bibes), with contributions from teams at the Laboratoire de Physique des Solides in Orsay (Xiaoyan Li, Alexandre Gloter) and the Institut Néel in Grenoble (Quintin N. Meier).

The work was supported by the Swiss National Science Foundation (Project No. P500PT_214449) and the European Research Council (ERC PoC UPLIFT Project No. 101113273).

Reference :
E. Gradauskaite et al., “Polarization Boost and Ferroelectricity Down to One Unit Cell in Layered Carpy-Galy La₂Ti₂O₇ Thin Films,” Advanced Materials 2025, 2416963, https://doi.org/10.1002/adma.202416963