Construction of a Microscopic Model for Yb and Tm Compounds on the Basis of a $\mib{j}$-$\mib{j}$ Coupling Scheme

TL;DR

This paper develops a microscopic $j$-$j$ coupling model for heavy lanthanide compounds like Yb and Tm, accurately capturing their electronic states and multipole behaviors, and validates it against detailed seven-orbital models.

Contribution

It introduces a $j$-$j$ coupling based microscopic model for Yb and Tm compounds, aligning well with complex seven-orbital models and enabling efficient analysis of multipole states.

Findings

The $j$-$j$ coupling model reproduces $f$-electron states accurately.

The model effectively describes low-temperature multipole states.

Multipole susceptibilities match those from more complex models.

Abstract

We provide a prescription to construct a microscopic model for heavy lanthanide systems such as Yb and Tm compounds by exploiting a $j$-$j$ coupling scheme. Here we consider a situation with a large spin-orbit coupling, in which $j$=5/2 sextet is fully occupied, while $j$=7/2 octet is partially occupied, where $j$ denotes total angular momentum. We evaluate crystalline electric field potentials and Coulomb interactions among the states of the $j$=7/2 octet to construct a local Hamiltonian in the $j$-$j$ coupling scheme. Then, it is found that the local $f$-electron states composed of the $j$=7/2 octet agree quite well with those of seven $f$ orbitals even for a realistic value of the spin-orbit coupling. As an example of the application of the present model, we discuss low-temperature multipole states of Yb- and Tm-based filled skutterudites by analyzing multipole susceptibility of the Anderson model in the $j$-$j$ coupling scheme with the use of a numerical renormalization group technique. From the comparison with the numerical results of the seven-orbital Anderson model, it is concluded that the multipole state is also well reproduced by the $j$-$j$ coupling model, even when we include the hybridization between conduction and $f$ electrons for the realistic value of the spin-orbit coupling. Finally, we briefly discuss future applications of the present prescription for theoretical research on heavy lanthanide compounds.