QUANTUM-THEORY OF LAYER VIBRATION IN THE LAYER-STRUCTURED FERMI FLUID

A method of introducing collective motion into the layered Fermi fluid (LFF) is discussed by concentrating on layer vibrations. By the random phase approximation (RPA), the original dynamical degrees of freedom of particles are separated into collective modes (CMs), uncorrelated (harmonic) oscillator modes (UOMs) and two-dimensional (2D) motions of particles within layers, which leads to a subband structure of particle spectrum. Transverse CMs cause the system's instability in case the interaction potential has too high a repulsive core. A primitive estimation of the correlation energy DELTAepsilon due to CMs is presented in the Hartree-Fock approximation for a simple toy model with a square well potential. \DELTAepsilon\ is shown to be maximized when CMs are sustained by about one half of particles. There exists a density above which the Fermi surface intersects the lowest two bands and the interaction among CMs and particles will become attractive to provide a possible mechanism of superfluidity and/or superconductivity.