Computer studies of system densities of states and of correlations in the excitation spectra of interacting electrons in disordered insulators

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Abstract
We have performed computer simulations of excitation spectra of interacting electrons in two- and three-dimensional disordered systems. The spectra of n-electron excitations was calculated in two dimensions and from it we obtained the system equilibrium properties: entropy, internal energy, and specific heat as functions of thermodynamic temperature. Two- and three-electron excitation spectra were studied emphasizing the correlational aspects. Our results clearly show that the Coulomb interactions strongly reduce the entropy at small internal energies, and enhance the specific heat at low temperatures. We have found that simultaneous two-electron excitations are important at low excitation energies, particularly in three dimensions, where they are comparable to the density of one-electron excitations. The spectrum of three-electron excitations in two dimensions was calculated and the results indicate that their density is lower than the density of two-electron excitations in two dimensions. The three-electron excitations in three dimensions at low excitation energies are comparable to the density of two-electron excitations in three dimensions, but more statistics are needed to confirm this result. Near zero excitation energy, the density of simultaneous excitations remains finite, while the density of sequential uncorrelated excitations tends to zero. The density of sequentially correlated excitations of two and three electrons was found to be small at very low energies, but increases rapidly with energy. The results indicate that dominant low-energy two- and three-electron excitations are cascade-type excitations.

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