Valence transition behavior of the doped Falicov-Kimball model at nonzero temperatures

TL;DR

This paper investigates how doping affects valence transitions in the spinless Falicov-Kimball model at nonzero temperatures, using exact-diagonalization and applying findings to real samarium compounds.

Contribution

It introduces a study of doping effects on valence transitions in the Falicov-Kimball model at finite temperatures, with specific focus on different doping types and comparison to experimental data.

Findings

Doping with non-magnetic ions alters $f$-state occupancy in predictable ways.

Theoretical results match well with experimental data on samarium hexaboride solid solutions.

Different doping types have opposite effects on valence transition behavior.

Abstract

The extrapolation of small-cluster exact-diagonalization calculations is used to study the influence of doping on valence transitions in the spinless Falicov-Kimball model at nonzero temperatures. Two types of doping are examined, and namely, the substitution of rare-earth ions by non-magnetic ions that introduce (i) one or (ii) none additional electron (per non-magnetic ion) into the conduction band. It is found that the first type of substitution increases the average $f$-state occupancy of rare-earth ions, whereas the second type of substitution has the opposite effect. The results obtained are used to describe valence transition behavior of samarium in the hexaboride solid solutions $Sm_{1-x}M_xB_6$ ($M=Y^{3+},La^{3+}, Sr^{2+},Yb^{2+}$) and a very good agreement of theoretical and experimental results is found.