The development of the materials and devices in this Letter was supported by the Vannevar Bush Faculty Fellowship programme sponsored by the Basic Research Office of the Assistant Secretary of Defense for Research and Engineering and funded by the US Office of Naval Research through grant N00014-15-1-2848. The neuromorphic aspects of this work, including the collaboration between UCSD and CNRS, were supported as part of the Quantum Materials for Energy Efficient Neuromorphic Computing, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under award DE-SC0019273. Part of the fabrication process was done at the San Diego Nanotechnology Infrastructure (SDNI) of UCSD, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the US National Science Foundation under grant ECCS-1542148. J.G.R. acknowledges support from FAPA and Colciencias number 120471250659. J.d.V. and J.T. thank Fundación Ramón Areces for their support with a postdoctoral fellowship. J.d.V. thanks I. Valmianski for helpful discussions.

Reviewer information

Nature thanks Kristjan Haule, Cheol Seong Hwang and the other anonymous reviewer(s) for their contribution to the peer review of this work.