Kavli Affiliate: Darrell G. Schlom
| First 5 Authors: Yilin Evan Li, Harikrishnan KP, Haidong Lu, Rachel A. Steinhardt, Megan E. Holtz
| Summary:
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.
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