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Phonon-limited valley lifetimes in single-particle bilayer graphene quantum dots

L. Banszerus1,2,*,†, K. Hecker1,2,*, L. Wang3, S. Möller1,2, K. Watanabe4, T. Taniguchi5, G. Burkard3, C. Volk1,2, and C. Stampfer1,2

  • *These authors contributed equally to this work.
  • †Present address: Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria.
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Phys. Rev. B 112, 035409 – Published 10 July, 2025

DOI: https://doi.org/10.1103/dkgn-pfjb

Abstract

The valley degree of freedom in two-dimensional (2D) semiconductors, such as gapped bilayer graphene (BLG) and transition metal dichalcogenides, is a promising carrier of quantum information in the emerging field of valleytronics. While valley dynamics have been extensively studied for moderate band gap 2D semiconductors using optical spectroscopy techniques, very little is known about valley lifetimes in narrow band gap BLG, which is difficult to study using optical techniques. Here, we report single-particle valley relaxation times T1 exceeding several microseconds in electrostatically defined BLG quantum dots using a pulse-gating technique. The observed dependence of T1 on perpendicular magnetic field can be understood qualitatively and quantitatively by a model in which T1 is limited by electron-phonon coupling. We identify the coupling to acoustic phonons via the bond length change and via the deformation potential as the limiting mechanisms.

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Phys. Rev. B 112, 035409– Published 10 July, 2025
  • Received 1 May 2024
  • Accepted 5 June 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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