Two-Channel Kondo Physics from Tunnelling Impurities with Triangular Symmetry

TL;DR

This paper demonstrates that tunnelling impurities with triangular symmetry can exhibit stable non-Fermi-liquid Kondo behavior, revealing a new class of impurity models with complex irrelevant operators and a rich phase diagram.

Contribution

It introduces a stable non-Fermi-liquid fixed point for impurities with triangular symmetry and analyzes its phase diagram, extending Kondo physics beyond traditional two-channel models.

Findings

Stable non-Fermi-liquid fixed point identified.

Four leading irrelevant operators influence temperature dependence.

Phase diagram features a critical manifold separating fixed points.

Abstract

Tunnelling impurities in metals have been known for some time to have the potential for exhibiting Kondo-like physics. However previous models based on an impurity hopping between two equivalent positions have run into trouble due to the existence of relevant operators that drive the system away from the non-Fermi-liquid Kondo fixed point. In the case of an impurity hopping among positions with higher symmetry, such as triangular symmetry, it is shown here that the non-Fermi-liquid behavior at low temperatures can be generic. Using various bosonization techniques, the fixed point is shown to be {\em stable}. However, unlike the conventional two-channel Kondo (2CK) model, it has {\em four} leading irrelevant operators, implying that while the form of the singular temperature dependence of physical quantities is similar to the 2CK model, there will not be simple universal amplitude ratios. The phase diagram of this system is analyzed and a critical manifold is found to separate the non-Fermi-liquid from a conventional Fermi liquid fixed point. Generalization to higher symmetries, such as cubic, and the possibility of physical realizations with dynamic Jahn-Teller impurities is discussed.