Plasmonic Nonreciprocity and Doppler Effect: The Role of Electron-Electron Interactions

Plasmonic modes propagating in the presence of an electrical DC current offer an appealing tool for achieving optical nonreciprocity at the nanoscale. This talk will discuss an approach relying on the DC-current-induced plasmonic Doppler effect, wherein downstream (upstream) propagation results in a blue (red) frequency shift of plasmon resonance, respectively. The carrier drift velocity in modern high-mobility two-dimensional electron systems can reach a substantial fraction of the Fermi velocity, leading to a strong Doppler effect. Since time reversal symmetry is broken in the presence of a flow, neither nonlinear coupling nor pumping, conventionally used to achieve nonreciprocity, are required in this case. We find that electron-electron interactions impact the magnitude of the effect, enhancing the Doppler shift substantially relative to the free-particle base value. Estimates of this effect based on Landau Fermi-liquid theory will be discussed and compared with the results of a microscopic approach.