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Locally enhanced conductivity due to the tetragonal domain structure in LaAlO3/SrTiO3 heterointerfaces

Abstract

The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the {001} interface of the band insulators LaAlO3 and TiO2-terminated SrTiO3 (STO; refs 1, 2). Transport and other measurements in this system show a plethora of diverse physical phenomena3,4,5,6,7,8,9,10,11,12,13,14. To better understand the interface conductivity, we used scanning superconducting quantum interference device microscopy to image the magnetic field locally generated by current in an interface. At low temperature, we found that the current flowed in conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background. The configuration of these paths changed on thermal cycling above the STO cubic-to-tetragonal structural transition temperature, implying that the local conductivity is strongly modified by the STO tetragonal domain structure. The interplay between substrate domains and the interface provides an additional mechanism for understanding and controlling the behaviour of heterostructures.

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Figure 1: Scanning SQUID measurements of current in LAO/STO heterostructures.
Figure 2: Current in unpatterned LAO/STO flows in narrow paths.
Figure 3: Tetragonal domain structure of STO is the origin of narrow paths of enhanced conductivity.
Figure 4: Schematic twin boundaries and domains in the STO crystal structure in the tetragonal phase.

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Acknowledgements

We thank G. A. Sawatzky, N. Pavlenko, S. Ilani, Y. Yacoby and A. Vailionis for discussions, Y. Yeshurun and E. Zeldov for use of their optical set-ups, J. Drori, D. Hadad and Y. Shperber for their assistance with the optical measurements and M. E. Huber for assistance in SQUID design and fabrication. S. Ilani and collaborators have performed complementary measurements by local electrostatic imaging. This work was primarily supported by the Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under contract DE-AC02-76SF00515. B.K. acknowledges support from FENA and the EC grant no. FP7-PEOPLE-2012-CIG-333799. Y.W.X. acknowledges partial support from the US Air Force Office of Scientific Research (FAQSSO-10-1-0524). J.M. acknowledges financial support by the German Science Foundation (TRR80).

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B.K., E.M.S., H.N., J.R.K. and K.C.N. performed the SQUID measurements. B.K. performed polarized-light measurements. B.K., E.M.S. and J.R.K. analysed the data with input from K.A.M. C.B., H.K.S., Y.X., M.H. and Y.H. grew samples H1–H5. C.W., G.P. and R.J. grew samples M1 and M2. E.M.S., B.K. and K.A.M. prepared the manuscript with input from all co-authors. H.Y.H., J.M. and K.A.M. guided the work.

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Correspondence to Beena Kalisky or Kathryn A. Moler.

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Kalisky, B., Spanton, E., Noad, H. et al. Locally enhanced conductivity due to the tetragonal domain structure in LaAlO3/SrTiO3 heterointerfaces. Nature Mater 12, 1091–1095 (2013). https://doi.org/10.1038/nmat3753

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