Quasiparticle band structure

A specific tool to investigate the very existence of quasiparticles is photoemission spectroscopy in which the time evolution of the system with one removed particle is measured, and when this state evolves as a coherent superposition of oscillations of approximately the same frequency, it corresponds to the propagation of a quasiparticle with a reasonably well defined energy and a sufficiently long life-time. The independent-particle approximation is the main component of computational approaches of the band structure of solids. Among these computational approaches, schemes based on the density functional theory (DFT) have proven to be very successful and are by far the most widely used approach for quantitative calculations of realistic systems. Materials for which this rudimentary mean-field description of e?e interaction is sufficient have broad energy bands associated with large values of the kinetic energy of the electrons.