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Observation of a marginal Fermi glass

Nature Physics volume 17, pages 627–631 (2021)Cite this article

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Abstract

A long-standing open problem in condensed-matter physics is whether or not a strongly disordered interacting insulator can be mapped to a system of effectively non-interacting localized excitations. Using terahertz two-dimensional coherent spectroscopy, we investigate this issue in phosphorus-doped silicon, a classic example of a correlated disordered electron system in three dimensions. Despite the intrinsically disordered nature of these materials, we observe coherent excitations and strong photon echoes that provide us with a powerful method for the study of their decay processes. We extract the energy relaxation and decoherence rates close to the metal–insulator transition. We observe that both rates are linear in excitation frequency with a slope close to unity. The energy relaxation timescale counterintuitively increases with increasing temperature, and the coherence relaxation timescale has little temperature dependence below 25 K, but increases as the material is doped towards the metal–insulator transition. Here we argue that these features imply that the system behaves as a well-isolated electronic system on the timescales of interest, and relaxation is controlled by electron–electron interactions. Our observations constitute a distinct phenomenology, driven by the interplay of strong disorder and strong electron–electron interactions, which we dub the marginal Fermi glass.

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Fig. 1: Linear and nonlinear optical response of phosphorus-doped silicon.
Fig. 2: Two-dimensional terahertz spectra at different phosphorus concentrations.
Fig. 3: Frequency and doping dependence of the pump–probe and rephasing relaxation rates.
Fig. 4: Temperature dependence of the pump–probe and rephasing anti-diagonal spectra.

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Data availability

All data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank A. Burin, Y. Galperin, Y.-B. Kim, A. Legros, I. Martin, A. Millis, V. Oganesyan, S. Paramesweran, B. Shklovskii and Y. Yuan for helpful discussions. This project was supported by a now-cancelled DARPA DRINQS programme grant and by the Gordon and Betty Moore Foundation, EPiQS initiative, grant number GBMF-9454. S.G. acknowledges support from NSF grant no. DMR-1653271.

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Authors and Affiliations

  1. Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, USA

    Fahad Mahmood, Dipanjan Chaudhuri & N. P. Armitage

  2. Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, USA

    Fahad Mahmood

  3. F. Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL, USA

    Fahad Mahmood

  4. Department of Engineering Science and Physics, CUNY College of Staten Island, Staten Island, NY, USA

    Sarang Gopalakrishnan

  5. Initiative for Theoretical Sciences, The Graduate Center, CUNY, New York, NY, USA

    Sarang Gopalakrishnan

  6. Department of Physics and Center for Theory of Quantum Matter, University of Colorado Boulder, Boulder, CO, USA

    Rahul Nandkishore

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  5. N. P. Armitage
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Contributions

F.M. and D.C. built the 2D terahertz set-up and carried out experiments and analysis. S.G. and R.N. provided theoretical support. N.P.A. directed the project. All authors contributed to the writing and editing of the manuscript.

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Correspondence to Fahad Mahmood or N. P. Armitage.

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Supplementary Sections I–IV and Figs. 1–10.

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Mahmood, F., Chaudhuri, D., Gopalakrishnan, S. et al. Observation of a marginal Fermi glass. Nat. Phys. 17, 627–631 (2021). https://doi.org/10.1038/s41567-020-01149-0

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