Two Unanticipated Discoveries in the Electron Gas―Excitonic Collective Mode and Excitron

Abstract

Based on a nonperturbative scheme to determine the self-energy with automatically satisfying the Ward identity and the total-momentum conservation law, a fully self-consistent calculation is done in the electron gas at various temperatures to obtain the one-electron spectral function to find a novel low-energy peak, dubbed excitron, in addition to the quasiparticle peak and one- and two-plasmon high-energy satellites. This excitron emerges due to the short-range electron-hole-pair multiple excitation, an incipient stage of the excitonic collective mode which was also discovered recently in the dynamic structure factor in the low-density electron gas.