Figure 13.

a) Nano‐infrared imaging of charge‐transfer plasmon polaritons in WO_x/graphene heterostructures. “Programmable” nano‐patterned WO_x/graphene heterostructures exhibit b) confined plasmonic nano‐cavity modes and c) whispering‐gallery modes. Images in a)‐c) reproduced with permission.^{[ 113 ]} Copyright 2023, Springer Nature. d) Electronically‐induced topological transition and exceptional‐point singularities in coupled plasmon‐phonon modes of WO_x/graphene/a‐MoO₃ heterostructures. Reproduced under the terms of the CC‐BY 4.0 license.^{[ 177 ]} Copyright 2022, The Authors, Published by Springer Nature.