Competition between disorder and Coulomb interaction in a two-dimensional plaquette Hubbard model

Abstract

We have studied a disordered Nc × Nc plaquette Hubbard model on a two-dimensional square lattice at half-filling using a coherent potential approximation (CPA) in combination with a singlesite dynamical mean field theory (DMFT) approach with a paramagnetic bath. Such a model conveniently interpolates between the ionic Hubbard model at Nc = √ 2 and the Anderson model at Nc = ∞ and enables the analysis of the various limiting properties. We confirmed that within the CPA approach a band insulator behavior appears for non-interacting strongly disordered systems with a small plaquette size Nc = 4, while the paramagnetic Anderson insulator with nearly gapless density of states is present for large plaquette sizes Nc = 48. When the interaction U is turned on in the strongly fluctuating random potential regions, the electrons on the low energy states push each other into high energy states in DMFT in a paramagnetic bath and correlated metallic states with a quasiparticle peak and Hubbard bands emerge, though a larger critical interaction U is needed to obtain this state from the paramagnetic Anderson insulator (Nc = 48) than from the band insulator (Nc = 4). Finally, we observe a Mott insulator behavior in the strong interaction U regions for both Nc = 4 and Nc = 48 independent of the disorder strength. We discuss the application of this model to real materials.

Charge ordering and correlation effects in the extended Hubbard model

“…These results demonstrate how a system can be driven to a metallic behavior by increasing a local on-site repulsion, and are in stark contrast to the Mott insulating behavior induced by the same strong electron-electron interactions in the absence of non-local interactions, which has been extensively studied in the V = 0 model. 64 Such interaction-induced metallic behavior is reminiscent of the physics of the ionic Hubbard model, [97][98][99] where a band-insulator to metal transition is induced by strong electron-electron interactions. However, in contrast to the extended Hubbard model, the band insulating behavior of the ionic model is generated by a periodic external potential, rather than by non-local electron-electron interactions.…”

Local Spectroscopies Reveal Percolative Metal in Disordered Mott Insulators

“…Transport measurements help determine whether the states are localized or extended, and indeed corroborate a metallic state with a finite resistivity extrapolated to T = 0 in the Ru substituted compounds. Theoretical methods ranging from inhomogeneous mean field theory [10], DMFT-based approaches [11][12][13][14][15][16][17], to quantum Monte Carlo [18][19][20], and exact diagonalization studies [21] of the Anderson-Hubbard model also support the presence of insulator-metal transition (IMT). However the mechanism behind such a transition and the nature of the emergent metallic phase is unclear.…”

Formation of an incoherent metallic state in Rh-doped Sr2IrO4

“…Although there would be a finite density of states at E F for a purely disorder-driven Anderson insulator, including long range electronic correlations would open a soft Coulomb gap on the insulating side of the transition [27] and corrections to the density of states mimicking a pseudogap on the metallic side [28]. More recently, the effect of short-range Coulomb interactions, which is most relevant for this correlated systems, has been investigated theoretically, and soft Hubbard gaps were predicted [29,30]. Experimentally, disordered correlated systems are rare [31] and this system offers a good opportunity to test this behavior.…”