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Exciton condensation and perfect Coulomb drag

Nature volume 488, pages 481484 (23 August 2012) | Download Citation

Abstract

Coulomb drag is a process whereby the repulsive interactions between electrons in spatially separated conductors enable a current flowing in one of the conductors to induce a voltage drop in the other1,2,3. If the second conductor is part of a closed circuit, a net current will flow in that circuit. The drag current is typically much smaller than the drive current owing to the heavy screening of the Coulomb interaction. There are, however, rare situations in which strong electronic correlations exist between the two conductors. For example, double quantum well systems can support exciton condensates, which consist of electrons in one well tightly bound to holes in the other4,5,6. ‘Perfect’ drag is therefore expected; a steady transport current of electrons driven through one quantum well should be accompanied by an equal current of holes in the other7. Here we demonstrate this effect, taking care to ensure that the electron–hole pairs dominate the transport and that tunnelling of charge between the quantum wells, which can readily compromise drag measurements, is negligible. We note that, from an electrical engineering perspective, perfect Coulomb drag is analogous to an electrical transformer that functions at zero frequency.

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Acknowledgements

We thank A.H. MacDonald and D. Pesin for discussions. This work was supported by NSF grant DMR-1003080.

Author information

Affiliations

  1. Condensed Matter Physics, California Institute of Technology, Pasadena, California 91125, USA

    • D. Nandi
    • , A. D. K. Finck
    •  & J. P. Eisenstein
  2. Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA

    • L. N. Pfeiffer
    •  & K. W. West

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Contributions

D.N., A.D.K.F. and J.P.E. conceived the project. L.N.P. and K.W.W. grew the samples. D.N. and A.D.K.F. performed the experiment and, along with J.P.E., analysed the data and wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to J. P. Eisenstein.

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https://doi.org/10.1038/nature11302

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