Metal–Insulator Transition in the Two-Orbital Hubbard Model at Fractional Band Fillings: Self-Energy Functional Approach

We use the embedding approach for a dynamical mean-field method to investigate the electronic properties of a semi-infinite two-band Hubbard model at half and quarter fillings. Two effects determine the degree of correlation at the surface: first, there will charge transfer between the surface and the bulk, and, second, electrons at the surface are less delocalized due to the reduced coordination number. We determine the result of these two effects and compute the quasiparticle weight. It is shown that depletion of charge from the surface to the bulk at quarter filling competes with enhanced correlation effects; the net result is that at quarter filling, the quasiparticle weight at the surface is approximately equal to the bulk quasiparticle weight. Only when the charge transfer approaches zero at large interaction strengths does the quasiparticle weight at the surface become lower than that in the bulk.

Section: Resultsmentioning

confidence: 99%

Competition between reduced delocalization and charge transfer effects for a two-band Hubbard model

Nourafkan

Marsiglio

2011

“…It is metallic at weak coupling and Mott insulating at strong coupling as expected, whereas in an intermediate U -regime, an orbital-selective Mott phase appears where the Mott-gap opens only in the narrow band. 4,17,[24][25][26][27] It is not a priori evident what happens to the OSM phase for finite V .…”

Section: A the Phase Diagram At Half-fillingmentioning

confidence: 99%

Hybridizing localized and itinerant electrons: A recipe for pseudogaps

Winograd

Medici

2014

In a system where selective Mott localization is realized, some electrons show a gap to charge excitations while others do not. A hybridization between these two kind of electrons will lead to a smoothening of this sharp difference and can even bring the system back to a complete delocalization. We show here that there is a large region of parameters at finite hybridization where the selective localization persists and the system shows a partial filling of the selective gap with incoherent states, giving rise to a pseudogap. This result is illustrated here in a two orbital Hubbard model with Hund's coupling, but is based on quite general assumptions and should hold for a larger class of systems, and possibly be a paradigm for the pseudogap mechanism in cuprates.

“…By making use of the DMFT, the two-orbital Hubbard model has been studied by many groups. 12,[36][37][38][39][40][41][42][43] These calculations are either based on a semicircular density of states, which corresponds to the Bethe lattice, or they employ an impurity solver with certain limitations in temperature or interaction strength. Here, we solve the DMFT equation at finite dimension and temperatures.…”

Section: Applicationmentioning

confidence: 99%

Efficient treatment of the high-frequency tail of the self-energy function and its relevance for multiorbital models

Hanke

2012

In this paper, we present an efficient and stable method to determine the one-particle Green's function in the hybridization-expansion continuous-time (CT-HYB) quantum Monte Carlo method, within the framework of the dynamical mean-field theory (DMFT). The high-frequency tail of the impurity self-energy is replaced with a noise-free function determined by a dual-expansion around the atomic limit. This method does not depend on the explicit form of the interaction term. More advantageous, it does not introduce any additional numerical cost to the CT-HYB simulation. We discuss the symmetries of the two-particle vertex, which can be used to optimize the simulation of the four-point correlation functions in the CT-HYB. Here, we adopt it to accelerate the dual-expansion calculation, which turns out to be especially suitable for the study of material systems with complicated band structures. As an application, a two-orbital Anderson impurity model with a general on-site interaction form is studied. The phase diagram is extracted as a function of the Coulomb interactions for two different Hund's coupling strengths. In the presence of the hybridization between different orbitals, for smaller interaction strengths, this model shows a transition from metal to band-insulator. Increasing the interaction strengths, this transition is replaced by a crossover from Mott-insulator to band-insulator behavior.