Ultrafast plasmon thermalization in epitaxial graphene probed by time-resolved THz spectroscopy

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Epitaxial growth of graphene on silicon carbide (SiC) provides a unique opportunity to prepare and study several carbon allotropes. The Si-face of SiC can host four allotropes, namely buffer layer (BL), single-layer graphene (SLG), quasi-freestanding SLG (QFSLG), quasi-freestanding bilayer graphene (QFBLG), while the C-face hosts the multilayer epitaxial graphene (MEG). The graphene on SiC provides several routes for strong light-matter interaction in the far-infrared and terahertz spectral range.

The Epitaxial graphene (EG) films are inherently inhomogeneous due to the discontinuous domains, wrinkles, and substrate terraces. Hence, the carrier confinement potentials, which activate localized plasmons, emerge naturally in EG due to these inhomogeneities. In contrast, such confinement effects are often achieved artificially by intentional patterning of graphene films. This seminar will discuss the robust plasmonic response and pump-induced transparency at THz frequencies in various EG allotropes with the help of time-resolved terahertz and multi-THz spectroscopies. The study reveals the evolution of graphene plasmonic response (conductivity spectra) due to optical excitation on a picosecond timescale and its direct correlation with the transient temperature (and chemical potential) of the heated electronic subsystem. The access to carrier temperature also helps us understand the energy dissipation mechanisms in electronic and lattice subsystems relevant in Femto-nanosecond timescales.

References
[1] M. M. Jadidi et al., Nonlinear Terahertz Absorption of Graphene Plasmons, Nano Lett., 16, 2734 (2016).
[2] V. C. Paingad et al., Ultrafast plasmon thermalization in epitaxial graphene probed by time-resolved THz spectroscopy, Adv. Funct. Mater. 31, 2105763 (2021).