Three-way interplay among plasmons, electron-hole pairs, and light: coherent electromagnetic design for efficient...

Plasmon-driven hot-carrier generation (HCG) is entering a new stage: performance is not determined only by local absorption, but can be shaped by coherent electromagnetic design. Recent experiments show that (i) coupling plasmons to optical cavities and (ii) introducing controlled interactions among plasmons produce hybridized collective modes and reorganize optical eigenstates. These modes extend coherence areas beyond isolated near-field hot spots, enable an antenna-like redistribution of electromagnetic energy, and can substantially increase the yieldper absorbed excitation photon(apparent quantum efficiency, AQE), making coherence a practical design principle for plasmon-driven energy conversion. At the same time, this progress brings out a deeper microscopic question:photocurrent generation per incident photon, when normalized byopticalabsorption (often discussed as theinternal quantum efficiency), can show strong mode-dependent structures that are not fully captured by pictures based on local absorption or Landau-damping-based relaxation alone. In this Perspective, we organize these observations by introducing a hierarchy of coherence that follows the energy-conversion pathway from electromagnetic mode formation to microscopic electronic excitation. We show that cavity-mediated coherence and inter-plasmon coherence mainly determine plasmonic mode formation and electromagnetic energy redistribution, and therefore largely control the system-level AQE. By contrast, the mode selectivity seen in optical-absorption-normalized efficiencies points to a different conversion-stage mechanism-plasmon-electron-hole coherence-by which collective plasmonic excitations couple selectively to electronic channels inside metals. In this view, plasmon-driven HCG involves multiple, physically distinct coherence mechanisms that may act independently or interact coherently. This hierarchy-of-coherence perspective summarizes recent experimental and theoretical progress, clarifies both the power and the limitations of absorption-based intuition, and motivates the development of unified quantum approaches beyond Poisson-equation-based models for mode-specific plasmon-electron-hole coupling and for the predictive design of coherently engineered plasmonic energy-conversion systems.