Experimental signatures of the transition from acoustic plasmon to electronic sound in graphene

David Barcons Ruiz; Niels C.H. Hesp; Hanan Herzig Sheinfux; Carlos Ramos Marimón; Curdin Martin Maissen; Alessandro Principi; Reza Asgari; Takashi Taniguchi; Kenji Watanabe; Marco Polini; Rainer Hillenbrand; Iacopo Torre; Frank H.L. Koppens

doi:10.1126/sciadv.adi0415

Journal article Experimental signatures of the transition from acoustic plasmon to electronic sound in graphene

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David Barcons Ruiz, Niels C.H. Hesp, Hanan Herzig Sheinfux, Carlos Ramos Marimón, Curdin Martin Maissen, Alessandro Principi, Reza Asgari, Takashi Taniguchi, Kenji Watanabe, Marco Polini, Rainer Hillenbrand, Iacopo Torre, Frank H.L. Koppens. Experimental signatures of the transition from acoustic plasmon to electronic sound in graphene. Science Advances. 2023, 9 (39), eadi0415. https://doi.org/10.1126/sciadv.adi0415

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Fermi liquids respond differently to perturbations depending on whether their frequency is larger (collisionless regime) or smaller (hydrodynamic regime) than the inter-particle collision rate. This results in a different phase velocity between the collisionless zero sound and hydrodynamic first sound. We performed terahertz photocurrent nanoscopy measurements on graphene devices, with a metallic gate in close proximity to the sample, to investigate acoustic plasmons, the counterpart of sound modes in electronic Fermi liquids. We report the observation of a change in the phase velocity of acoustic plasmons in graphene when the excitation frequency approaches the electron- electron collision rate. This first observation of the first sound mode in an electronic Fermi liquid is of fundamental interest and can enable novel terahertz emitter and detection concepts.

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