Kondo effect in flux phases

TL;DR

This paper investigates the Kondo effect in a two-dimensional flux phase model, revealing a quantum phase transition at finite coupling, with unique scaling behaviors and a multichannel nature due to relativistic fermion spinor structure.

Contribution

It introduces a large-N analysis of the Kondo effect in a relativistic flux phase, highlighting a finite-coupling phase transition and multichannel characteristics.

Findings

A zero-temperature phase transition at finite coupling.

Kondo energy scales linearly with the distance to the transition.

Logarithmic corrections to scaling are present, indicating an upper critical dimension.

Abstract

We consider a band of fermions in two space dimensions with a flux phase (relativistic) dispersion relation coupled to a local magnetic impurity via an $ s-d$ interaction. This model describes spinons of a flux phase and it is also a qualitative model of the quasiparticles in a $d_{x^2-y^2}$ superconductor. We find a zero-temperature phase transition at a finite coupling constant between a weak coupling unscreened impurity state and a strong coupling regime with a Kondo effect. We use large-$N$ methods to study the phase transition in this Kondo system away from marginality. The Kondo energy scales linearly with the distance to the transition . The zero-field magnetic suceptibility at zero temperature diverges linearly. Similar behavior is found in the $T$-matrix which shows a resonance at the Kondo scale. However, in addition to this simple scaling, we always find the presence of logarithmic corrections-to-scaling. Such behavior is typical of systems at an upper critical dimension. We derive an effective fermion model in one space dimension for this problem. Unlike the usual Kondo problem, this system has an intrinsic multichannel nature which follows from the spinor structure of $2+1$-dimensional relativistic fermions.