Using Epitaxial Engineering to Statically Unleash Hidden Ground States in Oxide Heterostructures
Darrell G. Schlom 1 2
Guided by theory, unparalleled properties in oxide heterostructures—those of hidden ground states—are being unleashed in the static realm by exploiting epitaxial engineering. One method is strain engineering, where the misfit strain imposed by an underlying substrate makes it is possible to strain oxide thin films to percent levels—far beyond where they would crack or plastically deform in bulk. Other static methods we have been utilizing are epitaxial stabilization, dimensional confinement, and polarization doping. Three examples utilizing a mix of these static techniques of controlling structure will be shown in hopes of stimulating a discussion of related opportunities utilizing dynamic optical methods. These examples are (1) transmuting a material (EuTiO3) that is not ferroelectric or ferromagnetic in its unstrained state, into a ground state that is both at the same time; (2) utilizing a combination of strain and dimensional confinement to create a tunable dielectric (Sr7Ti6O19) with world record figure of merit at room temperature; and (3) epitaxial stabilization of rumpling in combination with polarization doping to create a strong magnetically-ordered ferroelectric at nearly room temperature in (LuFeO3)9/(LuFe2O4)1 superlattices.
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(2) C.H. Lee, N.D. Orloff, T. Birol, Y. Zhu, V. Goian, E. Rocas, R. Haislmaier, E. Vlahos, J.A. Mundy, L.F. Kourkoutis, Y. Nie, M.D. Biegalski, J. Zhang, M. Bernhagen, N.A. Benedek, Y. Kim, J.D. Brock, R. Uecker, X.X. Xi, V. Gopalan, D. Nuzhnyy, S. Kamba, D.A. Muller, I. Takeuchi, J.C. Booth, C.J. Fennie, and D.G. Schlom, Nature502 (2013) 532-536.
(3) J.A. Mundy, C.M. Brooks, M.E. Holtz, J.A. Moyer, A.F. Rebola, H. Das, S.M. Disseler, J.T. Heron, R. Held, R. Hovden, E. Padgett, Q. Mao, H. Paik, R. Misra, J.A. Borchers, W.D. Ratcliff, L.F. Kourkoutis, C.J. Fennie, P. Schiffer, D.A. Muller, and D.G. Schlom (unpublished).