Plasmon modes represent a second kind of possible elementary excitation for the Fermi liquid. Basically, plasmon modes involve a cooperative motion of the system, governed by the global interaction between the charge carriers. Plasmon modes in two-dimensional electron liquids illustrate a long-wavelength dispersion that can be captured by classical equations of motion. The dispersion, however, departs from its classical value, becoming sensitive to quantum effects, by increasing the plasmon momentum.
The response of electron systems to electrodynamic fields that change rapidly in space is endowed by unique features, including an exquisite spatial nonlocality. This can reveal much about the materials’ electronic structure that is invisible in standard probes that use gradually varying fields. In this talk, we will start by introducing the plasmonics both in single and double layer graphene and describe the quantum non-locality effects in graphene plasmonics. Our theory involves three types of nonlocal quantum effects: single-particle velocity matching, interaction-enhanced Fermi velocity, and interaction-reduced compressibility. The near-field imaging experiments reveal a parameter-free match with the full quantum description of the massless Dirac electron gas.
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