Mixed-valent regime of the two-channel Anderson impurity as a model for UBe_13

TL;DR

This paper explores the mixed-valent regime of a two-channel Anderson impurity model for uranium ions, revealing non-Fermi-liquid behavior and explaining magnetic susceptibility data in UBe_13 with a new computational approach.

Contribution

It introduces a novel Monte Carlo and non-crossing approximation method to analyze the mixed-valent regime, identifying critical non-Fermi-liquid fixed points and energy scales.

Findings

Discovery of a non-Fermi-liquid fixed point with two-channel Kondo behavior

Identification of distinct energy scales for doublet screening

Support for quadrupolar-Kondo interpretation of UBe_13 magnetic susceptibility

Abstract

We investigate the mixed-valent regime of a two-configuration Anderson impurity model for uranium ions, with separate quadrupolar and magnetic doublets. With a new Monte Carlo approach and the non-crossing approximation we find: (i) A non-Fermi-liquid fixed point with two-channel Kondo model critical behavior; (ii) Distinct energy scales for screening the low-lying and excited doublets; (iii) A semi-quantitative explanation of magnetic-susceptibility data for U$_{1-x}$Th$_x$Be$_{13}$ assuming 60-70% quadrupolar doublet ground-state weight, supporting the quadrupolar-Kondo interpretation.