Orbital Localization and Delocalization Effects in the U 5f^2 Configuration: Impurity Problem

TL;DR

This paper investigates how localized and delocalized U 5f-orbitals influence the impurity physics in a metal, revealing complex fixed point behavior and magnetic susceptibility effects through numerical renormalization group analysis.

Contribution

It introduces a model considering both localized and delocalized U 5f-orbitals, highlighting their impact on impurity fixed points and magnetic properties, which was not addressed in previous models.

Findings

Fixed points exhibit residual local spins and phase shifts.

Phase shift varies between 0 and π/2, indicating competing fixed points.

Impurity magnetic susceptibility reflects the competition between fixed points.

Abstract

Anderson models, based on quantum chemical studies of the molecule of U(C_8H_8)_2, are applied to investigate the problem of an U impurity in a metal. The special point here is that the U 5f-orbitals are divided into two subsets: an almost completely localized set and a considerably delocalized one. Due to the crystal field, both localized and delocalized U 5f-orbitals affect the low-energy physics. A numerical renormalization group study shows that every fixed point is characterized by a residual local spin and a phase shift. The latter changes between 0 and \pi/2, which indicates the competition between two different fixed points. Such a competition between the different local spins at the fixed points reflects itself in the impurity magnetic susceptibility at high temperatures. These different features cannot be obtained if the special characters of U 5f-orbitals are neglected.