# Exploring the Kondo effect of an extended impurity with chains of Co adatoms in a magnetic field

## TL;DR

This paper investigates the magnetic field-induced Kondo effect in finite Co adatom chains, revealing how level crossings create effective impurities that produce Kondo resonances, supported by quantum Monte Carlo simulations.

## Contribution

It introduces a model of extended impurities at level crossings in Co chains and demonstrates the Kondo effect through numerical simulations, linking theory with STM experiments.

## Key findings

- Kondo resonance appears at sites with dominant Kondo coupling
- Quantum Monte Carlo accurately reproduces field-dependent STM signals
- Level crossings induce effective two-level systems acting as impurities

## Abstract

Motivated by recent STM experiments, we explore the magnetic field induced Kondo effect that takes place at symmetry protected level crossings in finite Co adatom chains. We argue that the effective two-level system realized at a level crossing acts as an extended impurity coupled to the conduction electrons of the substrate by a distribution of Kondo couplings at the sites of the chain. Using auxiliary-field quantum Monte Carlo simulations, which quantitatively reproduce the field dependence of the zero-bias signal, we show that a proper Kondo resonance is present at the sites where the effective Kondo coupling dominates. Our modeling and numerical simulations provide a theoretical basis for the interpretation of the STM spectrum in terms of level crossings of the Co adatom chains.