Fig. 12: Acoustic plasmons for ultrasensitive sensing and quantum applications.

a Acoustic plasmons in graphene for ultrasensitive infrared spectroscopy⁶⁸. The architectural configuration of the acoustic plasmon resonator, illustrating coupling pathways to plasmon modes under normal incidence of a TM polarized plane wave. Red and green arrows signify AGPs and conventional GPs, respectively. The inset displays typical plasmon dispersions for AGPs and GPs in the free-standing scenario. b Schematic of the device structure. c The mechanism for plasmonic absorption enhancement using the quarter-wavelength condition. d Ångström-thick film sensing using the AGP sensor. Reproduced with permission⁶⁸. Copyright 2019 Springer Nature Limited. e Graphene acoustic plasmons for revealing quantum surface-response of metals¹²³. Schematics of a dielectric-graphene–dielectric–metal heterostructure. The zoom-in view presents surface-response functions, namely d_⊥ and d_∥, alongside corresponding microscopic parameters defining the metal surface: equilibrium electronic density, n₀(z), and induced charge density, ρ_ind(z). f Employing the spectral shifting of AGPs to extract the quantum surface-response of metals. Reproduced with permission¹²³. Copyright 2021 Springer Nature Limited.