Renormalization of the spectrum of in-depth excitations below the Fermi level in a two-dimensional electron system with strong interaction

The dependence of quasiparticle Fermi energy on electron density is investigated by analyzing radiative recombination spectra of two-dimensional electrons with photoexcited holes bound to remote acceptors. This method enables us to measure the dependence of renormalized quasiparticle mass on the concentration of two-dimensional electrons. It is established that with decreasing electron density (increasing parameter ${r}_s$ up to 4.5) the density-of-states effective mass of quasiparticles increases by 35% compared to the cyclotron electron mass. It is shown that in a perpendicular magnetic field the concept of quasiparticles in a two-dimensional Fermi liquid is applicable not only near the Fermi level but also deep below the Fermi surface, down to the bottom of the size-quantization band, since the broadening of excitations appears to be much less than their energy. The effective mass and broadening of quasiparticles were found to be significantly dependent on their energy measured from the Fermi surface down to the very bottom of the size-quantization band.