Local quantum critical behavior in magnetic Kondo impurity models with partially screened moment

TL;DR

This paper investigates local quantum criticality in magnetic Kondo impurity models with partially screened moments, revealing a residual symmetry and singular spectral features, and discusses implications for related quantum systems.

Contribution

It derives an effective resonant level model for the underscreened Kondo impurity and identifies a local quantum critical behavior caused by a bound state with residual symmetry.

Findings

Residual $Z_2$ symmetry leads to a $ ext{delta}$-resonance at the Fermi level.

Logarithmic singularity in impurity spin susceptibility as a function of $ ext{max}( ext{omega}, T)$.

Magnetic field breaks symmetry and suppresses the singularity.

Abstract

In the strong coupling limit, an effective resonant level model is derived for the spin-1 underscreened Kondo impurity model. A local quantum critical behavior is induced by the formation of a bound state with partially screened magnetic moment, displaying a residual $Z_2$ symmetry, leading to a $\delta $-resonance at the Fermi level in the impurity spectral function. As a consequence, a logarithmic singularity appears in the real part of the impurity dynamic spin susceptibility as a function of $\max (\omega, T)$, with $\omega $ as frequency, $T$ temperature. A small magnetic field breaks this $Z_2$ symmetry and suppresses the singularity. We also discuss the possible manifestation of such a quantum critical behavior in the spin-1/2 two Kondo impurity model and the single quantum dot system with even electron occupation.