Polar metals by geometric design

T. H. Kim, D. Puggioni, Y. Yuan, L. Xie, H. Zhou, N. Campbell, P. J. Ryan, Y. Choi, J. W. Kim, J. R. Patzner, S. Ryu, J. P. Podkaminer, J. Irwin, Y. Ma, C. J. Fennie, M. S. Rzchowski, X. Q. Pan, V. Gopalan, J. M. Rondinelli, C. B. Eom

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Abstract

Gauss's law dictates that the net electric field inside a conductor in electrostatic equilibrium is zero by effective charge screening; free carriers within a metal eliminate internal dipoles that may arise owing to asymmetric charge distributions. Quantum physics supports this view, demonstrating that delocalized electrons make a static macroscopic polarization, an ill-defined quantity in metals - it is exceedingly unusual to find a polar metal that exhibits long-range ordered dipoles owing to cooperative atomic displacements aligned from dipolar interactions as in insulating phases. Here we describe the quantum mechanical design and experimental realization of room-temperature polar metals in thin-film ANiO 3 perovskite nickelates using a strategy based on atomic-scale control of inversion-preserving (centric) displacements. We predict with ab initio calculations that cooperative polar A cation displacements are geometrically stabilized with a non-equilibrium amplitude and tilt pattern of the corner-connected NiO 6 octahedra - the structural signatures of perovskites - owing to geometric constraints imposed by the underlying substrate. Heteroepitaxial thin-films grown on LaAlO 3 (111) substrates fulfil the design principles. We achieve both a conducting polar monoclinic oxide that is inaccessible in compositionally identical films grown on (001) substrates, and observe a hidden, previously unreported, non-equilibrium structure in thin-film geometries. We expect that the geometric stabilization approach will provide novel avenues for realizing new multifunctional materials with unusual coexisting properties.

Original languageEnglish (US)
Pages (from-to)68-72
Number of pages5
JournalNature
Volume533
Issue number7601
DOIs
StatePublished - May 5 2016

All Science Journal Classification (ASJC) codes

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    Kim, T. H., Puggioni, D., Yuan, Y., Xie, L., Zhou, H., Campbell, N., Ryan, P. J., Choi, Y., Kim, J. W., Patzner, J. R., Ryu, S., Podkaminer, J. P., Irwin, J., Ma, Y., Fennie, C. J., Rzchowski, M. S., Pan, X. Q., Gopalan, V., Rondinelli, J. M., & Eom, C. B. (2016). Polar metals by geometric design. Nature, 533(7601), 68-72. https://doi.org/10.1038/nature17628