Quantum interference in an interfacial superconductor

Abstract

The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO)1 has several intriguing properties2,3,4,5,6 that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (Tc; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-Tc superconductors8. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.

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Figure 1: Device description and V(Φ) oscillations.
Figure 2: I(Φ) oscillations and kinetic inductance in C-SQUIDs.
Figure 3: Tunable Josephson junctions in E-SQUIDs.
Figure 4: Controllable asymmetry in E-SQUIDs.

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Acknowledgements

We thank T. Klapwijk, A. Geresdi, A. Akhmerov, A. Brinkman and J. Mannhart for useful discussions and feedback about the preliminary results. This work was supported by The Netherlands Organisation for Scientific Research (NWO/OCW) as part of the Frontiers of Nanoscience program, the Dutch Foundation for Fundamental Research on Matter (FOM), the Deutsche Forschungsgemeinschaft (DFG) via Project KO 1303/13-1 and EU-FP6-COST Action MP1308.

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E.M. fabricated the devices. S.G. performed the transport measurements with help from E.M. S.G. and A.M.R.V.L.M. analysed the data. R.W., R.K. and D.K. carried out the numerical simulations and Y.M.B. provided theoretical support. L.M.K.V. and A.D.C. supervised the project. S.G. wrote the manuscript with input from all co-authors.

Corresponding authors

Correspondence to Srijit Goswami or Andrea D. Caviglia.

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The authors declare no competing financial interests.

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Goswami, S., Mulazimoglu, E., Monteiro, A. et al. Quantum interference in an interfacial superconductor. Nature Nanotech 11, 861–865 (2016). https://doi.org/10.1038/nnano.2016.112

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