Tunable electron–flexural phonon interaction in graphene heterostructures

Mir Mohammad Sadeghi, Yajie Huang, Chao Lian, Feliciano Giustino, Emanuel Tutuc, Allan H. MacDonald, Takashi Taniguchi, Kenji Watanabe and Li Shi ()
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Mir Mohammad Sadeghi: The University of Texas at Austin
Yajie Huang: The University of Texas at Austin
Chao Lian: The University of Texas at Austin
Feliciano Giustino: The University of Texas at Austin
Emanuel Tutuc: The University of Texas at Austin
Allan H. MacDonald: The University of Texas at Austin
Takashi Taniguchi: National Institute for Materials Science
Kenji Watanabe: National Institute for Materials Science
Li Shi: The University of Texas at Austin

Nature, 2023, vol. 617, issue 7960, 282-286

Abstract: Abstract Peculiar electron–phonon interaction characteristics underpin the ultrahigh mobility1, electron hydrodynamics2–4, superconductivity5 and superfluidity6,7 observed in graphene heterostructures. The Lorenz ratio between the electronic thermal conductivity and the product of the electrical conductivity and temperature provides insight into electron–phonon interactions that is inaccessible to past graphene measurements. Here we show an unusual Lorenz ratio peak in degenerate graphene near 60 kelvin and decreased peak magnitude with increased mobility. When combined with ab initio calculations of the many-body electron–phonon self-energy and analytical models, this experimental observation reveals that broken reflection symmetry in graphene heterostructures can relax a restrictive selection rule8,9 to allow quasielastic electron coupling with an odd number of flexural phonons, contributing to the increase of the Lorenz ratio towards the Sommerfeld limit at an intermediate temperature sandwiched between the low-temperature hydrodynamic regime and the inelastic electron–phonon scattering regime above 120 kelvin. In contrast to past practices of neglecting the contributions of flexural phonons to transport in two-dimensional materials, this work suggests that tunable electron–flexural phonon coupling can provide a handle to control quantum matter at the atomic scale, such as in magic-angle twisted bilayer graphene10 where low-energy excitations may mediate Cooper pairing of flat-band electrons11,12.

Date: 2023
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DOI: 10.1038/s41586-023-05879-y

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