We investigate the influence of electron-electron interactions on the conductance of two-dimensional disordered spinless electrons. We present an efficient numerical method based on diagonalization in a truncated basis of Hartree-Fock states to determine with high accuracy the low-energy properties in the entire parameter space. We find that weak interactions increase the d.c. conductance in the strongly localized regime while they decrease the d.c. conductance for weak disorder. Strong interactions always decrease the conductance. We also study the localization of single-particle excitations at the Fermi energy which turns out to be only weakly influenced by the interactions. 71.55.Jv, 72.15.Rn, 71.30.+h The influence of electron-electron interactions on the transport in disordered electronic systems has been investigated intensively within the last two decades [1,2]. Recently, the problem has reattracted a lot of attention after experimental [3] and theoretical [4] results challenged established opinions.It is well accepted [5] that non-interacting electrons in three dimensions (3D) undergo a localizationdelocalization transition at finite disorder. In contrast, all states are localized in 2D and 1D even for infinitesimal weak disorder [6]. However, today it is believed that the metal-insulator transition (MIT) in most experimental systems cannot be explained based on noninteracting electrons. The metallic phase of disordered interacting electrons has been studied intensively within the perturbative renormalization group (RG) [2] leading to a qualitative analysis of the MIT and the identification of different universality classes. One of the results is that the lower critical dimension of the MIT is d − c = 2 as it is for non-interacting electrons. Therefore it came as a surprise when experiments [3] on Si-MOSFETs revealed indications of a MIT in 2D. Since these experiments are performed at low electron density where the Coulomb interaction is particularly strong compared to the Fermi energy, interaction effects are a likely reason for this MIT. A complete understanding has, however, not yet been obtained. Explanations were suggested based on the perturbative RG [7], non-perturbative effects [8], or the transition being a superconductor-insulator transition rather than a MIT [9].Theoretically, surprising results have been obtained for just two interacting particles in the insulating regime [4]. It was found that two particles can form a pair whose localization length is much larger than that of a single particle. Later an even larger delocalization was suggested for clusters of three or more particles [10]. In the case of a repulsive electron-electron these delocalized states have rather high energy, thus their relevance for the low-energy properties of a degenerate system is not clear. It has been argued that the many-particle problem can be reduced to a few interacting quasiparticles above the Fermi surface [11]. This is, however, only possible, if the interactions do not change the nature of the ground s...

We study the influence of electron-electron interactions on the electronic properties of disordered materials. In particular, we consider the insulating side of a metal-insulator transition where screening breaks down and the electron-electron interaction remains long-ranged. The investigations are based on the quantum Coulomb glass, a generalization of the classical Coulomb glass model of disordered insulators. The quantum Coulomb glass is studied by decoupling the Coulomb interaction by means of a Hartree-Fock approximation and exactly diagonalizing the remaining localization problem. We investigate the behavior of the Coulomb gap in the density of states when approaching the metal-insulator transition and study the influence of the interaction on the localization of the electrons. We find that the interaction leads to an enhancement of localization at the Fermi level. 71.55.Jv, 72.15.Rn, 71.30.+h

No abstract

No abstract

The combined influence of disorder and interactions on the transport properties of electrons in one dimension is investigated. The numerical simulations are carried out by means of the Hartree-Fock-based diagonalization (HFD), a very efficient method to determine the low-energy properties of a disordered many-particle system. We find that the conductance of a strongly localized system can become considerably enhanced by the interactions. The enhancement for long-range interactions is significantly larger than for short-range interactions. In contrast, the conductance of weakly localized systems becomes suppressed by the interactions.