The emergence of classical behavior in magnetic adatoms

TL;DR

This paper investigates how increasing coupling strength in magnetic adatoms suppresses quantum spin tunneling, leading to the emergence of classical magnetic behavior through environmental decoherence.

Contribution

It demonstrates how stronger spin-environment interactions cause the quenching of quantum tunneling, resulting in classical magnetization in magnetic adatoms.

Findings

Quantum spin tunneling is suppressed by increased coupling.

Environmental decoherence leads to classical magnetic states.

Spontaneous magnetization emerges as QST is quenched.

Abstract

A wide class of nanomagnets shows striking quantum behavior, known as quantum spin tunneling (QST): instead of two degenerate ground states with opposite magnetizations, a bonding-antibonding pair forms, resulting in a splitting of the ground state doublet with wave functions linear combination of two classically opposite magnetic states, leading to the quenching of their magnetic moment. Here we study how QST is destroyed and classical behavior emerges in the case of magnetic adatoms, as the strength of their coupling, either to the substrate or to each other, is increased. Both spin-substrate and spin-spin coupling renormalize the QST splitting to zero allowing the environmental decoherence to eliminate superpositions between classical states, leading to the emergence of spontaneous magnetization.