Slave Boson Analysis on $f^2$-Configuration System with $\Gamma_1$ Singlet Crystalline-Electric-Field Ground State in Cubic Symmetry

TL;DR

This paper uses slave boson formalism to analyze the phase diagram of an $f^2$-configuration system with cubic symmetry, revealing multiple phases, phase transitions, and heavy quasiparticle behavior.

Contribution

It introduces an extended three-orbital Anderson model and uncovers new phase structures and transitions in $f^2$ systems with crystalline-electric-field effects.

Findings

Identified three zero-temperature phases: $$ CEF singlet and two Fermi liquids.

Discovered first-order transitions including charge-transfer and energy-level crossing.

Observed heavy quasiparticles with peak mass enhancement in intermediate valence region.

Abstract

We investigated electron phases in the $f^2$-configuration system with the $\Gamma_1$ crystalline-electric-field (CEF) ground state in cubic symmetry. An extended three-orbital periodic Anderson model, which consists of $j=5/2$ states, is evaluated by using the rotationally invariant slave boson formalism. As a result, we found three phases at zero temperature: the $\Gamma_1$ CEF singlet phase, and two kinds of Fermi liquid (FL). One of the FL arises owing to the presence of the $\Gamma_5$ CEF state, while the other forms a quasi-degenerated CEF state. All these phases are separated by first-order transitions: the charge-transfer transition and the CEF energy-level crossing. We also found heavy quasiparticle behaviors in the intermediate valence region between the $f^2$ and $f^3$ configurations. In this region, the mass enhancement factor exhibits a peak structure by increasing the hybridization. Physical properties of these phases and transitions are discussed.