Correlations in a band insulator

Abstract

We study a model of a covalent band insulator with on-site Coulomb repulsion at half-filling using dynamical mean-field theory. Upon increasing the interaction strength the system undergoes a discontinuous transition from a correlated band insulator to a Mott insulator with hysteretic behavior at low temperatures. Increasing the temperature in the band insulator close to the insulator-insulator transition we find a crossover to a Mott insulator at elevated temperatures. Remarkably, correlations decrease the energy gap in the correlated band insulator. The gap renormalization can be traced to the low-frequency behavior of the self-energy, analogously to the quasiparticle renormalization in a Fermi liquid. While the uncorrelated band insulator is characterized by a single gap for both charge and spin excitations, the spin gap is smaller than the charge gap in the correlated system.

Fluctuation-driven topological Hund insulators

“…On the other hand, the inter-orbital repulsion tends to restore (2, 0). The Hund coupling J therefore plays the crucial role for favoring (1, 1) in the strong coupling region 45,46 . The effective reduction of the energy difference between the orbitals is the important prerequisite to get the topological phase in the intermediate region.…”

Strong electron correlations in FeSb2

“…In addition to the KI scenario, where the small semiconducting gap arises in a Kondo lattice due to the hybridization of the localized f (or d) state and a broad conduction band, Takahashi and Moriya (TM) [9], starting from the electronic structure as calculated for FeSi, have offered a different interpretation, where the unusual thermodynamics including magnetic susceptibility and specific heat can be well interpreted by using the spin fluctuation theory of itinerant electron systems. While also starting from a band insulator model, recent theoretical explorations [10,11,12] tend to treat FeSi and FeSb 2 as band insulators with strong local dynamical correlations, i.e., correlated band insulators (CBI) in a more general physical interpretation. This approach, which takes the local correlations into account via a dynamical mean-field approximation (DMFT [13]), can also explain all major physical properties of FeSb 2 as well as FeSi [10].…”

Magnetic transition in a correlated band insulator

“…1 has been previously studied within the DMFT formalism [9], with a model hybridizing two bands with identical, semielliptical density of states. DMFT finds a scenario remarkably similar to the one observed for the metalinsulator case in the standard single band model at halffilling: a first order transition between band and Mott insulator characterized by a discontinuous change in the double occupancy.…”

“…Local moments: Within DMFT [9], the phase boundary is determined by a discontinuity in the double occupancy d, the latter being related to the local moment m by,…”