Article
Data availability
Data presented in the main figures of the manuscript are available from
the authors upon reasonable request.
Acknowledgements We thank L. O. Chua and H. S. P. Wong for comments on the
manuscript. We also thank K. J. Cremata, A. L. D. Kilcoyne, T. Tyliszczak, D. Shapiro,
G. Gibson, X. Sheng and J. Zhang for assistance in collecting experimental data or
construction of the models. We acknowledge S. M. Bohaichuk, J. C. Nino, A. Conklin and
J. L. Andrews for discussions on specific topics and suggestions for illustrations. Work was
performed in part in the nano@Stanford labs, which are supported by the National Science
Foundation under award ECCS-1542152. Synchrotron measurements were conducted at the
Advanced Light Source, a US DOE Office of Science User Facility under contract no.
DE-AC02-05CH11231, and at the Stanford Synchrotron Radiation Lightsource, SLAC National
Accelerator Laboratory, a US DOE Office of Science User Facility under contract no.
DE-AC02-76SF00515. R.S.W. acknowledges the X-Grants Program of the President’s
Excellence Fund at Texas A&M University.Author contributions S.K. and R.S.W. conceived the project and planned the various
measurements. Z.W. performed the materials growth, compositional analysis and parts of the
chip fabrication. S.K. and Z.W. performed the in operando spectroscopic measurements and
collected the electrical data. S.K. and R.S.W. constructed the model and wrote the manuscript.
Competing interests The authors declare no competing interests.Additional information
Supplementary information is available for this paper at https://doi.org/10.1038/s41586-020-
2735-5.
Correspondence and requests for materials should be addressed to S.K.
Peer review information Nature thanks Adnan Mehonic, Syed Ghazi Sarwat and the other,
anonymous, reviewer(s) for their contribution to the peer review of this work.
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