Observation of polar vortices in oxide superlattices

A. K. Yadav, C. T. Nelson, S. L. Hsu, Z. Hong, J. D. Clarkson, C. M. Schlepuëtz, A. R. Damodaran, P. Shafer, E. Arenholz, L. R. Dedon, D. Chen, A. Vishwanath, A. M. Minor, L. Q. Chen, J. F. Scott, L. W. Martin, R. Ramesh

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348 Scopus citations

Abstract

The complex interplay of spin, charge, orbital and lattice degrees of freedom provides a plethora of exotic phases and physical phenomena. In recent years, complex spin topologies have emerged as a consequence of the electronic band structure and the interplay between spin and spin-orbit coupling in materials. Here we produce complex topologies of electrical polarization-namely, nanometre-scale vortex-antivortex (that is, clockwise-anticlockwise) arrays that are reminiscent of rotational spin topologies-by making use of the competition between charge, orbital and lattice degrees of freedom in superlattices of alternating lead titanate and strontium titanate layers. Atomic-scale mapping of the polar atomic displacements by scanning transmission electron microscopy reveals the presence of long-range ordered vortex-antivortex arrays that exhibit nearly continuous polarization rotation. Phase-field modelling confirms that the vortex array is the low-energy state for a range of superlattice periods. Within this range, the large gradient energy from the vortex structure is counterbalanced by the corresponding large reduction in overall electrostatic energy (which would otherwise arise from polar discontinuities at the lead titanate/strontium titanate interfaces) and the elastic energy associated with epitaxial constraints and domain formation. These observations have implications for the creation of new states of matter (such as dipolar skyrmions, hedgehog states) and associated phenomena in ferroic materials, such as electrically controllable chirality.

Original languageEnglish (US)
Pages (from-to)198-201
Number of pages4
JournalNature
Volume530
Issue number7589
DOIs
StatePublished - Feb 11 2016
Externally publishedYes

Bibliographical note

Funding Information:
Acknowledgements A.K.Y. and R.R. acknowledge support from the Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231), for the synthesis and characterization of superlattices. R.R. and C.T.N. acknowledge support from the Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231), for TEM characterization of superlattices. S.L.H. acknowledges support from the National Science Foundation under the MRSEC program (DMR-1420620). Z.H. acknowledges support from the National Science Foundation (DMR-1210588). J.D.C. acknowledges support from the Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231). C.M.S. acknowledges use of the Advanced Photon Source, which was supported by the US Department of Energy, Office of Science, Office of Basic Energy Science (DE-AC02-06CH11357), for the synchrotron-based reciprocal space map studies of superlattice structures at Sector 33-BM-C beamline. A.R.D. acknowledges support from the Army Research Office (W911NF-14-1-0104). P.S. and E.A. acknowledge support from the Director, Office of Science, Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231), for the synchrotron-based studies of the superlattice structures. L.R.D. acknowledges support from the US Department of Energy, Office of Basic Energy Sciences (DE-SC0012375) for the chemical analysis of the superlattice structures. D.C. acknowledges support from the National Science Foundation under the MRSEC program (DMR-1420620). A.V. and A.M.M. acknowledge support from Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231). L.Q.C. acknowledges support from the National Science Foundation (DMR-1210588). L.W.M. acknowledges support from the National Science Foundation (DMR-1451219). Electron microscopy of superlattice structures was performed at the Molecular Foundry, LBNL, supported by the Office of Science, Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231). Z.H. thanks J. Britson, F. Xue and J. Wang for help and discussions.

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