Chirality is a geometrical property by which an object is not super-imposable onto its mirror image, thereby imparting a handedness. Chirality determines many important properties in nature—from the strength of the weak interactions according to the electroweak theory in particle physics to the binding of enzymes with naturally occurring amino acids or sugars, reactions that are fundamental for life. In condensed matter physics, the prediction of topologically protected magnetic skyrmions and related spin textures in chiral magnets has stimulated significant research. If the magnetic dipoles were replaced by their electrical counterparts, then electrically controllable chiral devices could be designed. Complex oxide BaTiO3/SrTiO3 nanocomposites and PbTiO3/SrTiO3 superlattices are perfect candidates, since “polar vortices,” in which a continuous rotation of ferroelectric polarization spontaneously forms, have been recently discovered. Using resonant soft X-ray diffraction, we report the observation of a strong circular dichroism from the interaction between circularly polarized light and the chiral electric polarization texture that emerges in PbTiO3/SrTiO3 superlattices. This hallmark of chirality is explained by a helical rotation of electric polarization that second-principles simulations predict to reside within complex 3D polarization textures comprising ordered topological line defects. The handedness of the texture can be topologically characterized by the sign of the helicity number of the chiral line defects. This coupling between the optical and novel polar properties could be exploited to encode chiral signatures into photon or electron beams for information processing.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Jan 30 2018|
Bibliographical noteFunding Information:
ACKNOWLEDGMENTS. We acknowledge discussions with Gerrit van der Laan, Maurits W. Haverkort, and Fernando Etayo. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract DE-AC02-05CH11231. Electron microscopy of superlattice structures was performed at the Molecular Foundry, Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, US Department of Energy under Contract DE-AC02-05CH11231. P.G.-F. recognizes support from Ramón y Cajal Grant RyC-2013-12515. A.R.D. acknowledges support from the Army Research Office under Grant W911NF-14-1-0104 and the US Department of Energy, Office of Basic Energy Sciences under Grant DE-SC0012375 for synthesis and structural study of the materials. A.K.Y. and C.T.N. were supported by the Office of Basic Energy Sciences, US Department of Energy under Contract DE-AC02-05CH11231. S.-L.H. acknowledges support from the National Science Foundation under the Materials Research Science and Engineering Centers program under Grant DMR-1420620. J.Í. acknowledges support from the Luxembourg National Research Fund under Grant C15/MS/10458889 NEWALLS. P.G.-F. and J.J. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through Grant FIS2015-64886-C5-2-P. R.R. and L.W.M. acknowledge support from the Gordon and Betty Moore Foundation’s Emergent Phenomena in Quantum Systems Initiative, under Grant GBMF5307.
- Electric polarization
- Resonant soft X-ray diffraction
- Second-principles calculations
- Topological textures