Small Energy Scale for Mixed-Valent Uranium Materials

TL;DR

This paper models mixed-valent uranium materials using a two-channel Anderson impurity model, revealing a small energy scale and non-Fermi liquid behavior that could explain experimental observations in UBe$_{13}$.

Contribution

It introduces a detailed impurity model for uranium compounds and uncovers a universal scaling behavior near a non-Fermi liquid crossover.

Findings

Crossover to non-Fermi liquid state below temperature T*

T* scales with the triplet-doublet splitting to the 7/2 power

Universal scaling functions describe magnetic susceptibility

Abstract

We investigate a two-channel Anderson impurity model with a $5f^1$ magnetic and a $5f^2$ quadrupolar ground doublet, and a $5f^2$ excited triplet. Using the numerical renormalization group method, we find a crossover to a non-Fermi liquid state below a temperature $T^*$ varying as the $5f^2$ triplet-doublet splitting to the 7/2 power. To within numerical accuracy, the non-linear magnetic susceptibility and the $5f^1$ contribution to the linear susceptibility are given by universal one-parameter scaling functions. These results may explain UBe$_{13}$ as mixed valent with a small crossover scale $T^*$.