Effect of Anharmonicity on the Kondo Phenomena of a Magnetic Ion Vibrating in a Confinement Potential

TL;DR

This paper investigates how anharmonic cage potentials influence Kondo phenomena in vibrating magnetic ions, revealing continuous crossovers, local Fermi liquid ground states, and potential routes to two-channel Kondo effects.

Contribution

It introduces a detailed analysis of anharmonic cage potentials using numerical renormalization group, highlighting new crossover behaviors and phase transitions in Kondo regimes.

Findings

Continuous crossover among Kondo regimes in double-well potentials.

Ground state remains a local Fermi liquid across parameter space.

Quantum phase transition to odd parity state with increased Coulomb interaction.

Abstract

Effect of anharmonicity of a cage potential for a magnetic ion vibrating in a metal is investigated by the numerical renormalization group method. The cage potential is assumed to be one-dimensional and of the double-well type. In the absence of the Coulomb interaction, we find continuous crossover among the three limiting cases: Yu-Anderson-type Kondo regime, the double-well-type Kondo one, and the renormalized Fermi chain one. In the entire parameter space of the double-well potential, the ground state is described by a local Fermi liquid. In the Yu-Anderson-type Kondo regime, a quantum phase transition to the ground state with odd parity takes place passing through the two-channel Kondo fixed point when the Coulomb interaction increases. Therefore, the vibration of a magnetic ion in an oversized cage structure is a promising route to the two-channel Kondo effect.