Electron attraction mediated by Coulomb repulsion

Abstract

One of the defining properties of electrons is their mutual Coulomb repulsion. However, in solids this basic property may change; for example, in superconductors, the coupling of electrons to lattice vibrations makes the electrons attract one another, leading to the formation of bound pairs. Fifty years ago it was proposed1 that electrons can be made attractive even when all of the degrees of freedom in the solid are electronic, by exploiting their repulsion from other electrons. This attraction mechanism, termed ‘excitonic’, promised to achieve stronger and more exotic superconductivity2,3,4,5,6. Yet, despite an extensive search7, experimental evidence for excitonic attraction has yet to be found. Here we demonstrate this attraction by constructing, from the bottom up, the fundamental building block8 of the excitonic mechanism. Our experiments are based on quantum devices made from pristine carbon nanotubes, combined with cryogenic precision manipulation. Using this platform, we demonstrate that two electrons can be made to attract each other using an independent electronic system as the ‘glue’ that mediates attraction. Owing to its tunability, our system offers insights into the underlying physics, such as the dependence of the emergent attraction on the underlying repulsion, and the origin of the pairing energy. We also demonstrate transport signatures of excitonic pairing. This experimental demonstration of excitonic pairing paves the way for the design of exotic states of matter.

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Figure 1: Model system and experimental realization of its fundamental building block.
Figure 2: From repulsive to attractive electrons.
Figure 3: Dependence of pairing energy on the polarizer detuning and the origin of the pair binding energy.
Figure 4: Transport measurements.

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Acknowledgements

We thank E. Altman, E. Berg, Y. Gefen, M. Goldstein, U. Leonhardt, G. Refael and A. Yacoby for discussions and D. Mahalu for the e-beam writing. K.K. acknowledges support from the Carlsberg Foundation. Y.O. acknowledges support by Minerva, BSF and ERC Adg grant (FP7/2007-2013 340210). F.v.O. acknowledges support through SPP 1459 and SFB 658. S.I. acknowledges financial support by the ERC Cog grant (See-1D-Qmatter, No. 647413).

Reviewer Information Nature thanks R. Egger, T. Kontos and E. Scheer for their contribution to the peer review of this work.

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A.H., A.B., I.S. and S.I. performed the experiments, analysed the data, contributed to its theoretical interpretation and wrote the paper. I.S. built the scanning probe microscope. I.K. built the custom measurement instrumentation for the experiment. J.W. designed and fabricated the devices. K.K., Y.O. and F.v.O. developed the theoretical model. K.K. performed the theoretical simulations.

Corresponding author

Correspondence to S. Ilani.

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The authors declare no competing financial interests.

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This file contains Supplementary Text and Data, which includes Supplementary Methods, Supplementary Figures 1-10, a Supplementary Discussion and additional references. (PDF 2798 kb)

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Hamo, A., Benyamini, A., Shapir, I. et al. Electron attraction mediated by Coulomb repulsion. Nature 535, 395–400 (2016). https://doi.org/10.1038/nature18639

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