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Ultrafast terahertz photoconductivity and near-field imaging of nanoscale inhomogeneities in multilayer epitaxial graphene nanoribbons

Arvind Singh1, Jan Kunc2, Tinkara Troha1, Hynek Němec1, and Petr Kužel1,*

  • *Contact author: kuzelp@fzu.cz
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Phys. Rev. B 113, 115417 – Published 17 March, 2026

DOI: https://doi.org/10.1103/qzns-hs4t

Abstract

We study broadband terahertz (THz) conductivity and ultrafast photoconductivity spectra in lithographically fabricated multilayer epitaxial graphene nanoribbons grown on C-face of 6H-SiC substrate. THz near-field spectroscopy reveals local conductivity variations across nanoscale structural inhomogeneities such as wrinkles and grain boundaries within the multilayer graphene. Ultrabroadband THz far-field spectroscopy (0.15–16THz) distinguishes doped graphene layers near the substrate from quasineutral layers (QNLs) further from the substrate. Temperature-dependent THz conductivity spectra are dominated by intraband transitions both in the doped and QNLs. Photoexcitation then alters mainly the response of the QNLs: these exhibit very high carrier mobility and large positive THz photoconductivity with picosecond lifetime. The response of QNLs strongly depends on the carrier temperature Tc: the scattering time drops by an order of magnitude down to ∼10 fs upon an increase of Tc from 50 K to Tc>1000K, which is attributed to an enhanced electron-electron and electron-phonon scattering and to an interaction of electrons with mid-gap states.

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Phys. Rev. B 113, 115417– Published 17 March, 2026
  • Received 7 November 2025
  • Revised 28 January 2026
  • Accepted 26 February 2026
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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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