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Discovery of superconductivity in KTaO3 by electrostatic carrier doping


Superconductivity at interfaces has been investigated since the first demonstration of electric-field-tunable superconductivity in ultrathin films in 19601. So far, research on interface superconductivity has focused on materials that are known to be superconductors in bulk1,2,3,4,5,6,7,8,9. Here, we show that electrostatic carrier doping can induce superconductivity in KTaO3, a material in which superconductivity has not been observed before10,11. Taking advantage of the large capacitance of the self-organized electric double layer that forms at the interface between an ionic liquid and KTaO3 (ref. 12), we achieve a charge carrier density that is an order of magnitude larger than the density that can be achieved with conventional chemical doping. Superconductivity emerges in KTaO3 at 50 mK for two-dimensional carrier densities in the range 2.3 × 1014 to 3.7 × 1014 cm−2. The present result clearly shows that electrostatic carrier doping can lead to new states of matter at nanoscale interfaces.

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Figure 1: Electric double-layer (EDL) transistor.
Figure 2: Characterization of EDL transistors.
Figure 3: Transport properties.
Figure 4: Superconducting properties.
Figure 5: Transport properties and critical parameters of superconductivity.


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This work was partly supported by Grants-in-Aid for Scientific Research (21686002, 21224009 and 21654046) and an Innovative Area grant on ‘Topological Quantum Phenomena’ from the Ministry of Education, Culture, Sport, Science and Technology of Japan. This work was also partly supported by Asahi Glass Foundation and the Nippon Sheet Glass Foundation for Materials Science and Engineering.

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K.U. performed planning, sample fabrication, measurements and analysis. S.N., N.K., T.N. and H.A. assisted with cryogenic transport measurements. H.S. and H.T.Y. assisted with planning. Y.I. and M.K. performed planning and analysis.

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Correspondence to M. Kawasaki.

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The authors declare no competing financial interests.

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Ueno, K., Nakamura, S., Shimotani, H. et al. Discovery of superconductivity in KTaO3 by electrostatic carrier doping. Nature Nanotech 6, 408–412 (2011).

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