Intrinsic Origin of Enhancement of Ferroelectricity in SnTe Ultrathin Films

• Published in: Physical review letters Vol. 121; no. 2; p. 027601
• Main Authors: Liu, Kai, Lu, Jinlian, Picozzi, Silvia, Bellaiche, Laurent, Xiang, Hongjun
• Format: Journal Article
• Language: English
• Published: United States 13.07.2018
• DOI: 10.1103/physrevlett.121.027601

Previous studies showed that, as ferroelectric films become thinner, their Curie temperature (T_{c}) and polarization below T_{c} both typically decrease. In contrast, a recent experiment [Chang et al., Science 353, 274 (2016)SCIEAS0036-807510.1126/science.aad8609] observed that atomic-thick SnTe films have a higher T_{c} than their bulk counterpart, which was attributed to extrinsic effects. We find, using first-principles calculations, that the 0-K energy barrier for the polarization switching (which is a quantity directly related to T_{c}) is higher in most investigated defect-free SnTe ultrathin films than that in bulk SnTe, and that the 5-unit-cell (UC) SnTe thin film has the largest energy barrier as a result of an interplay between hybridization interactions and Pauli repulsions. Further simulations, employing a presently developed effective Hamiltonian, confirm that freestanding, defect-free SnTe thin films have a higher T_{c} than bulk SnTe, except for the 1-UC case. Our work, therefore, demonstrates the possibility to intrinsically enhance ferroelectricity of ultrathin films by reducing their thickness.