2014/05/13 by F. Delgado, F.S. Delgado, S. Loth +5
Chemistry · Physics and Astronomy · #Antibonding molecular orbital #Antiferromagnetism #Atomic orbital #Chemistry #Condensed matter physics #Degenerate energy levels #Electron #Exchange interaction #Ferromagnetism #Ground state #Magnetic field #Magnetic moment #Magnetic properties of thin films #Magnetization #Nanomagnet #Physics #Physics of Superconductivity and Magnetism #Quantum #Quantum and electron transport phenomena #Quantum mechanics #Spin (aerodynamics) #Superexchange #Thermodynamics #cond-mat.str-el
paper · pdf · doi:10.1209/0295-5075/109/57001
published as EPL 109, 57001 (2015) · 5 pages, 4 figures
arxiv created 2014/05/13 · openalex publication_date 2015/03/01 · arxiv updated 2015/03/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
A wide class of nanomagnets shows striking quantum behaviour, known as quantum spin tunnelling (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 behaviour emerges in the case of magnetic adatoms, where, contrary to larger nanomagnets, the QST splitting is in some instances bigger than temperature and broadening. We analyze two different mechanisms for the renormalization of the QST splitting: Heisenberg exchange between different atoms, and Kondo exchange interaction with the substrate electrons. Sufficiently strong 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. Importantly, we extract the strength of the Kondo exchange for various experiments on individual adatoms and construct a phase diagram for the classical to quantum transition.