Carrier excitation and decay processes in graphene are of broad interest since relaxation pathways that are not present in conventional materials are enabled by a gapless Dirac electronic band structure. Here, we report that a previously unobserved decay pathway—hot plasmon emission—results in Fermi-level-dependent mid-infrared emission in graphene. Our observations of non-thermal contributions to Fermi-level-dependent radiation are an experimental demonstration of hot plasmon emission arising from a photo-inverted carrier distribution in graphene achieved via ultrafast optical excitation. Our calculations indicate that the reported plasmon emission process can be several orders of magnitude brighter than Planckian emission mechanisms in the mid-infrared spectral range. Both the use of gold nanodisks to promote scattering and localized plasmon excitation and polarization-dependent excitation measurements provide further evidence for bright hot plasmon emission. These findings define an approach for future work on ultrafast and ultrabright graphene emission processes and mid-infrared light source applications.
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This work was supported by US Department of Energy Office of Science grant no. DE-FG02-07ER46405. V.W.B. was supported by a Defense Advanced Research Projects Agency Young Faculty Award (grant no. YFA D18AP00043) and by the Gordon and Betty Moore Foundation through a Moore Inventors Fellowship. S.K. acknowledges support by a Samsung Scholarship. Parts of the text and results reported in this work have been reproduced from the thesis by L. Kim, at the California Institute of Technology, and are accessible at https://thesis.library.caltech.edu/11500/.
The authors declare no competing interests.
Peer review information Nature Materials thanks Ortwin Hess, Frank Koppens and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Kim, L., Kim, S., Jha, P.K. et al. Mid-infrared radiative emission from bright hot plasmons in graphene. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-00935-2
Nature Materials (2021)