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; Li Shi

doi:10.1038/s41586-023-05879-y

Tunable electron-flexural phonon interaction in graphene heterostructures

Nature. 2023 May;617(7960):282-286. doi: 10.1038/s41586-023-05879-y. Epub 2023 Apr 26.

Authors

Mir Mohammad Sadeghi^#¹, Yajie Huang^#², Chao Lian^{3

4}, Feliciano Giustino^{3

4}, Emanuel Tutuc⁵, Allan H MacDonald³, Takashi Taniguchi⁶, Kenji Watanabe⁷, Li Shi^{8

9}

Affiliations

¹ Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA.
² Materials Science and Engineering Program, The University of Texas at Austin, Austin, TX, USA.
³ Department of Physics, The University of Texas at Austin, Austin, TX, USA.
⁴ Oden Institute for Computational Engineering and Science, The University of Texas at Austin, Austin, TX, USA.
⁵ Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX, USA.
⁶ International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan.
⁷ Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan.
⁸ Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA. lishi@mail.utexas.edu.
⁹ Materials Science and Engineering Program, The University of Texas at Austin, Austin, TX, USA. lishi@mail.utexas.edu.

^# Contributed equally.

PMID: 37100903
DOI: 10.1038/s41586-023-05879-y

Abstract

Peculiar electron-phonon interaction characteristics underpin the ultrahigh mobility¹, electron hydrodynamics^2-4, superconductivity⁵ and superfluidity^6,7 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 rule^8,9 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 couping 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 electrons^11,12.