title: Control of single-spin magnetic anisotropy by exchange coupling.
abstract: The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be affected strongly by this interaction. Although this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons in water molecules in a host's tissue. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data-storage devices, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magnetic anisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be renormalized controllably. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be tuned electronically. These effects may play a significant role in the development of spintronic devices in which an individual magnetic atom or molecule is coupled to conducting leads.
authors: 1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] Department of Physics and Astronomy, University College London, London WC1E 6BT, UK [3].
authors: Jenny C
authors: JC
authors: Oberg
authors: 1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] [3].
authors: M Reyes
authors: MR
authors: Calvo
authors: International Iberian Nanotechnology Laboratory, 4715-330 Braga, Portugal.
authors: Fernando
authors: F
authors: Delgado
authors: 1] Instituto de Nanociencia de Aragón and Laboratorio de Microscopías Avanzadas, Universidad de Zaragoza, 50018 Zaragoza, Spain [2] Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza, Spain.
authors: María
authors: M
authors: Moro-Lagares
authors: 1] Instituto de Nanociencia de Aragón and Laboratorio de Microscopías Avanzadas, Universidad de Zaragoza, 50018 Zaragoza, Spain [2] Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza, Spain.
authors: David
authors: D
authors: Serrate
authors: Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle, Germany.
authors: David
authors: D
authors: Jacob
authors: International Iberian Nanotechnology Laboratory, 4715-330 Braga, Portugal.
authors: Joaquín
authors: J
authors: Fernández-Rossier
authors: 1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] Department of Physics and Astronomy, University College London, London WC1E 6BT, UK [3] Department of Chemistry, University College London, London WC1H 0AJ, UK.
authors: Cyrus F
authors: CF
authors: Hirjibehedin