From Kondo effect to weak-link regime in quantum spin-1/2 spin chains

TL;DR

This paper investigates the transition from Kondo to weak-link regimes in a quantum spin-1/2 chain with tunable impurities, combining theoretical and numerical methods to analyze the Kondo screening cloud and its experimental observability.

Contribution

It introduces a model of tunable bond impurities in a spin chain and combines renormalization group with numerical calculations to study the Kondo length and crossover phenomena.

Findings

Kondo length is within experimental reach in ultracold-atom setups.

Asymmetry and magnetic fields cause redistribution of Kondo screening.

The crossover from Kondo to weak-link regimes is characterized by shrinking Kondo length.

Abstract

We analyze the crossover from Kondo to weak-link regime by means of a model of tunable bond impurities in the middle of a spin-1/2 XXZ Heisenberg chain. We study the Kondo screening cloud and estimate the Kondo length by combining perturbative renormalization group approach with the exact numerical calculation of the integrated real-space spin-spin correlation functions. We show that, when the spin impurity is symmetrically coupled to the two parts of the chain with realistic values of the Kondo coupling strengths and spin-parity symmetry is preserved, the Kondo length takes values within the reach of nowadays experimental technology in ultracold-atom setups. In the case of non-symmetric Kondo couplings and/or spin parity broken by a nonzero magnetic field applied to the impurity, we discuss how Kondo screening redistributes among the chain as a function of the asymmetry in the couplings and map out the shrinking of the Kondo length when the magnetic field induces a crossover from Kondo impurity to weak-link physics.