Breakdown of coherence in Kondo alloys: crucial role of concentration versus band filling

Abstract

We study the low energy states of the Kondo alloy model (KAM) as function of the magnetic impurity concentration per site, x, and the conduction electron average site occupation, nc. In previous works, two different Fermi liquid regimes had been identified at strong Kondo coupling JK , that may be separated by a transition at x = nc. Here, we analyze the KAM for finite JK on a Bethe lattice structure. First, using the meanfield coherent potential approximation (DMFT-CPA) which is exact at lattice coordination Z = ∞, we show that the real part of the local potential scattering may be located outside the conduction electron band, revealing a possible breakdown of Luttinger theorem for intermediate values of impurity concentration x. Unusual physical signatures are expected, e.g., in ARPES experiments. In order to take into account fluctuations associated with finite dimensionality, i.e. finite Z, we extend this analyze by also studying the KAM with an adaptation of the statistical-DMFT method that was developped elsewhere. We review the distributions of local potential scattering and their evolution with model parameters: concentration, strength of Kondo coupling, coordination number, local site neighborhood, connection with percolation issue. Relevence for Kondo alloys material with f -electrons is also discussed. arXiv:1810.05383v1 [cond-mat.str-el] 12 Oct 2018 1 n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D 0 0.2 0.4 0.6 0.8 1 n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D 0 0.25 0.5 0.75 1 n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D 0 0.25 0.5 0.75 1 n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D 0 0.25 0.5 0.75 1 n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D 0 0.25 0.5 0.75 1 n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D 0 0.25 0.5 0.75 1 n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D 0 0.25 0.5 0.75 1 n c = 0.25 n c = 0.5 n c = 0.75 J K = D J K = 2D J K = 5D 0 0.25 0.5 0.75 1

Photo-emission signatures of coherence breakdown in Kondo alloys: dynamical mean-field theory approach

“…These works motivated further theoretical investigations of the concomitant roles of x and n c in the issue of coherence in Kondo alloys. A transition or a crossover between dilute and coherent dense Kondo Fermi liquid regimes had been suggested by various complementary methods including mean-field approximation and strong coupling expansions [39,40,41,42,43,44,45], Monte Carlo simulations [46,47,48], numerical renormalization group [49], or local-moment approach [50,51]. A crucial difference between these two Kondo Fermi-liquid regimes can be obtained from strong coupling description: for x < n c each Kondo impurity captures one conduction electron, forming Kondo singlets, and the Fermi-liquid quasiparticles correspond to the remaining n c − x electrons.…”