Speaker:
Professor Philippe Ghosez, Theoretical Materials Physics, Université de Liège, Belgium
Abstract:
Although prototypical ferroelectrics such as BaTiO3 and PbTiO3 belong to the family of ABO3 perovskite compounds, relatively few perovskite oxides are in fact ferroelectrics [1]. Few years ago, a new type of improper ferroelectricity [2] – nowadays referred to as “hybrid improper ferroelectricity” [3] – in which the appearance of the polarization is driven by non-polar atomic motions has been identified in artificial superlattices [2,4,5,6] and naturally-layered Ruddlesden-Popper compounds [3,7]. On the one hand, design rules to engineer such a hybrid improper ferroelectricity have been proposed [6], opening alternative possibilities to create new ferroelectrics. On the other hand, the unusual coupling between polar and non-polar atomic motions in these compounds provided the opportunity to achieve new or enhanced multifunctional properties [2,3,5,8,9, 10].
The key feature of hybrid improper ferroelectrics is the presence in their free energy expansion of a trilinear term of the form “F = λ PR1R2”, which couples the polar distortion P to two other non-polar distortions R1 and R2 [7,10]. Independently of the primary order parameter and of the nature of the phase transition, this trilinear coupling of lattice modes appears by itself as a key feature to be exploited [8]. Most efforts have focused so far on systems in which R1 and R2 are antiferrodistortive oxygen-rotation motions [7,10]. However, trilinear terms can also couple the polarization to Jahn-Teller [11] or anti-polar distortions [12]. Focusing on recent results [13-
15] , I will discuss here how the trilinear coupling of the polarization with different Jahn-Teller distortions can produce unexpected phenomena and offers a concrete pathway to achieve electric control of electronic properties in some bulk and layered perovskites.
Work done in collaboration with J. Varignon, N. Bristowe, Karandeep, A. Mercy and E. Bousquet and supported by the F.R.S-FNRS project “HiT4FiT”. Ph. Ghosez also acknowledges a Research Professorship of the Francqui Foundation.
1. N. A. Benedek and C. J. Fennie, J. Phys. Chem. C 117, 13339 (2013).
2. E. Bousquet, et al. Nature 452, 732 (2008)
3. N. A. Benedek and C. J. Fennie, Phys. Rev. Lett. 106, 107204 (2011).
4. T. Fukushima, A. Stroppa, S. Picozzi and J. M. Perez-Mato, Phys. Chem. Chem. Phys. 13, 12186 (2011).
5. H. J. Zhao, W. Ren, Y. Yang, J. Iñiguez, X. M. Chen and L. Bellaiche, Nature Communications 1, 4021(2014).
6. J. M. Rondinelli and C. J. Fennie, Adv. Mat. 24, 1961 (2012).
7. N. Benedek, J. Rondinelli, H. Djani, Ph. Ghosez and Ph. Lightfoot, Dalton Transactions 44, 10543 (2015).
8. Ph. Ghosez and J.-M. Triscone, Nature Mater. 10, 269 (2011).
9. P. Aguado-Puente, P. García-Fernàndez, J. Junquera, Phys. Rev. Lett. 107, 217601(2011).
10. J. Varignon, N. C. Bristowe, E. Bousquet and Ph. Ghosez, C. R. Physique 16, 153(2015)
11. A. Stroppa, P. Barone, P. Jain, J. M. Perez-Mato and S. Picozzi, Adv. Mater. 25, 2284 (2013).
12. Y. Yang, J. Iñiguez, A.-J. Mao and L. Bellaiche, Phys. Rev. Lett. 112, 057202 (2014).
13. J. Varignon, N. C. Bristowe, E. Bousquet and Ph. Ghosez, Scientific Reports 5, 15364 (2015).
14. N. C. Bristowe, J. Varignon, D. Fontaine, E. Bousquet and Ph. Ghosez, , Nature Communications 6, 6677 (2015).
15. J. Varignon, N. C. Bristowe and Ph. Ghosez, available on arXiv:1505.03413.