Low-energy collective electronic excitations in a polaron gas

A dense gas of electrons whose effective mass is significantly enhanced at low frequencies is studied with the help of a simple classical analogy. The electromagnetic response is analyzed, and characteristic features are found in infrared-absorption and electron-energy-loss spectra. These spectral features arise from an additional light-absorbing excitation in midinfrared, and from a collective excitation (oscillation of the density of boson clouds) located in the far infrared.