%0 Journal Article
%A Gázquez Alabart, J.
%A Stengel, M.
%A Mishra, R.
%A Scigaj, M.
%A Varela Del Arco, María
%A Roldan, M. A.
%A Fontcuberta, J.
%A Sánchez, F.
%A Herranz, G.
%T Competition between polar and nonpolar lattice distortions in oxide quantum wells: new critical thickness at polar interfaces
%D 2017
%@ 0031-9007
%U https://hdl.handle.net/20.500.14352/18226
%X Two basic lattice distortions permeate the structural phase diagram of oxide perovskites: antiferrodistortive (AFD) rotations and tilts of the oxygen octahedral network and polar ferroelectric modes. With some notable exceptions, these two order parameters rarely coexist  in a bulk crystal, and understanding their competition is a lively area of active research. Here we demonstrate, by using the LaAlO₃/SrTiO₃ system as a test case, that quantum confinement can be a viable tool to shift the balance between AFD and polar modes and selectively stabilize one of the two phases. By combining scanning transmission electron microscopy (STEM) and first-principles-based models, we find a crossover between a bulklike LaAlO₃ structure where AFD rotations prevail, to a strongly polar state with no AFD tilts at a thickness of approximately three unit cells; therefore, in addition to the celebrated electronic reconstruction, our work unveils a second critical thickness, related not to the electronic properties but to the structural ones. We discuss the implications of these findings, both for the specifics of the LaAlO₃/SrTiO₃ system and for the general quest towards nanoscale control of material properties.
%~