Interband Coulomb Research Articles

One-dimensional two-band model of superconductivity

The interband Fermi surface nesting in the system of the title is shown to extremely magnify the effect of the exchange-like interaction which elevates the superconducting transition temperature T c by reducing the suppressing effect of the Coulomb interaction and in some cases drives superconductivity by itself. This magnification is through the processes expressed by the ladder and bubble diagrams including the interband Coulomb and exchange interactions in addition to the above one. The divergence of the present ladder diagram is new in the parameter-dependence and easier to occur than the known one taking account of the interband Coulomb interaction only. How this effective magnification of the above interaction elevates T c is roughly discussed. Relevance to the high T c of the YBa 2Cu 3O y superconductors is argued.

A diagrammatic method for a mixed valence hamiltonian

An approximate diagrammatic method is utilized to calculate the valence and densities of states of a two band system with inter- and intra-band Coulomb interactions at T = 0 K. The results indicate the existence of an intermediate valence state and a metal-insulator transition that can be continuous or discontinuous depending on the ratio G/ W; G is the inter-band Coulomb repulsion and W the conduction band half-width.

A new approach for the RFK model

We have studied the Ramirez-Falicov and Kimball (RFK) model for the intermediate valence problem, including a non-zero width ZW for the conduction band; a finite Coulomb repulsion between f electrons: U; and treated the inter-band Coulomb interaction G into an approach Hubbard I - style. We found that it is possible to obtain an abrupt valence transition for finite U, but not in the limit U → ∞. This discontinuous transition does not originate a fractionary occupancy of the f-level although an hybridization between f- and conductions electrons is included.

Mixed Valence and Spin States of the Two-Impurity System: New Hartree-Fock Ground States

New Hartree-Fock ground states are shown to result in the two-impurity Anderson model when coupled to boson-like interactions. The new states are asymmetric in both charge and spin in the two sites and exhibit the two types corresponding to the different exchange mechanisms. This situation in which two identical atoms behave as two unbalanced centers may have a variety of applications in condensed-matter physics such as valence fluctuations in solids. In this paper we analytically demonstrate the existence of new Hartree-Fock (HF) ground states in the two-impurity Anderson model with boson-like interac­ tion.*) The new ground states are asymmetric states in both charge and spin (staggered) in the two sites, which are stabilized below ferromagnetic and anti ferromagnetic coupling states only in the presence 0/ boson-like interac­ tion. We assert these spatially asymmetric ground states are a general con­ sequence of the systems describable by the present model and may relate to valence fluctuations in periodic systems such as certain rare-earth compounds. I) The boson-coupled Anderson model has been studied by Haldane 2 ) as a single impurity version of the Falicov-Kimball mode1. 3 ) He has found that in contrast to the conventional single-impurity Anderson mode1 4 ) the magnetic phase boundaries become the first-order transition lines when localized electrons are coupled with boson fields. This first-order transition at zero temperature (in parameter space) is equivalent in origin to that of Falicov-Kimball at finite temperatures due to interband Coulomb interaction in the composite periodic systems.

Magnetic susceptibility of FeSb 2 : A quasi-magnetic semiconductor

We study the magnetic susceptibility of FeSb 2 within a model of highly correlated valence band states and conduction electrons Coulomb interaction. Inter-band Coulomb and Hund type couplings are also considered. The latter are strong due to the d character of both valence and conduction bands edges. We suggest that the high susceptibility of FeSb 2( X ≈ 6×10 −4emu/mole) may be further enhanced by the addition of selected impurities, leading to a magnetic ground state.