Journal
PHYSICAL REVIEW LETTERS
Volume 120, Issue 22, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.120.227601
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Funding
- National Science Foundation [EFMA-1542741, DMR-1708615]
- King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) [OSR-2016-CRG5-2996]
- National Natural Science Foundation of China (NSFC) [61390502, 61505033]
- Army Research Office [W911NF-14-1-0104]
- Cornell Center for Materials Research
- NSF MRSEC program [DMR-1719875]
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Out-of-plane ferroelectricity with a high transition temperature in ultrathin films is important for the exploration of new domain physics and scaling down of memory devices. However, depolarizing electrostatic fields and interfacial chemical bonds can destroy this long-range polar order at twodimensional (2D) limit. Here we report the experimental discovery of the locking between out-of-plane dipoles and in-plane lattice asymmetry in atomically thin In2Se3 crystals, a new stabilization mechanism leading to our observation of intrinsic 2D out-of-plane ferroelectricity. Through second harmonic generation spectroscopy and piezoresponse force microscopy, we found switching of out-of-plane electric polarization requires a flip of nonlinear optical polarization that corresponds to the inversion of in-plane lattice orientation. The polar order shows a very high transition temperature (similar to 700 K) without the assistance of extrinsic screening. This finding of intrinsic 2D ferroelectricity resulting from dipole locking opens up possibilities to explore 2D multiferroic physics and develop ultrahigh density memory devices.
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