Enhanced electric conductivity at ferroelectric vortex cores in BiFeO3

Abstract

Topological defects in ferroic materials are attracting much attention both as a playground of unique physical phenomena and for potential applications in reconfigurable electronic devices. Here, we explore electronic transport at artificially created ferroelectric vortices in BiFeO3 thin films. The creation of one-dimensional conductive channels activated at voltages as low as 1 V is demonstrated. We study the electronic as well as the static and dynamic polarization structure of several topological defects using a combination of first-principles and phase-field modelling. The modelling predicts that the core structure can undergo a reversible transformation into a metastable twist structure, extending charged domain walls segments through the film thickness. The vortex core is therefore a dynamic conductor controlled by the coupled response of polarization and electron–mobile-vacancy subsystems with external bias. This controlled creation of conductive one-dimensional channels suggests a pathway for the design and implementation of integrated oxide electronic devices based on domain patterning.

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Figure 1: Electronic properties of topological defects in ferroelectrics.
Figure 2: Changes of the domain structure during measurement of the electronic properties of topological defects.
Figure 3: High resolution imaging of the observed domain wall twist.
Figure 4: DFT calculation of the electronic structure at the vortex.
Figure 5: Phase-field modelling of the vortex/antivortex domain arrangement.
Figure 6: Phase-field modelling of the locally biased vortex/antivortex domain arrangement.

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Acknowledgements

Experiments were conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, US Department of Energy. Support was provided by the Division of Scientific User Facilities (N.B.) and by the Materials Sciences and Engineering Division (S.V.K.) of the US Department of Energy, Basic Energy Sciences. B.W., J.B. and L.Q.C. are supported by US Department of Energy, Basic Sciences, under Grant No. DE-FG02-07ER46417. L.B. thanks mostly support from the Department of Energy, Office of Basic Energy Sciences, under contract ER-46612. L.B. also thanks the National Science Foundation grants DMR-1066158 and DMR-0701558, and Office of Naval Research grants N00014-11-1-0384, N00014-08-1-0915 and N00014-07-1-0825. Some computations were also made possible thanks to the National Science Foundation grant 0722625 and a challenge grant from the US Department of Defense. Y.H.C. acknowledges the support of the National Science Council, Republic of China, under contract NSC-100-2811-M-009-003. M.H. acknowledges support by the Netherlands Organization for Scientific Research (NWO) through a VENI grant.

Author information

N.B. and S.V.K. conceived and designed the experiments, and wrote the article. N.B. performed the experiments. B.W., J.B. and L.Q.C. performed phase-field modelling. W.R., L.B. and I.K. performed DFT calculations. A.N.M. and E.A.E. provided analytical theory for vortex structure and vacancy segregation. M.H., Y.H.C. and R.R. contributed materials and S.J. developed spectroscopic measurement technique and analysis tools. S.V.K., P.M. and R.K.V. co-wrote the article. All authors discussed the results and commented on the manuscript.

Correspondence to Nina Balke or Sergei V. Kalinin.

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Balke, N., Winchester, B., Ren, W. et al. Enhanced electric conductivity at ferroelectric vortex cores in BiFeO3. Nature Phys 8, 81–88 (2012) doi:10.1038/nphys2132

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