Stabilizing the magnetic moment of single holmium atoms by symmetry

Abstract

Single magnetic atoms, and assemblies of such atoms, on non-magnetic surfaces have recently attracted attention owing to their potential use in high-density magnetic data storage and as a platform for quantum computing. A fundamental problem resulting from their quantum mechanical nature is that the localized magnetic moments of these atoms are easily destabilized by interactions with electrons, nuclear spins and lattice vibrations of the substrate. Even when large magnetic fields are applied to stabilize the magnetic moment, the observed lifetimes remain rather short (less than a microsecond). Several routes for stabilizing the magnetic moment against fluctuations have been suggested, such as using thin insulating layers between the magnetic atom and the substrate to suppress the interactions with the substrate's conduction electrons, or coupling several magnetic moments together to reduce their quantum mechanical fluctuations. Here we show that the magnetic moments of single holmium atoms on a highly conductive metallic substrate can reach lifetimes of the order of minutes. The necessary decoupling from the thermal bath of electrons, nuclear spins and lattice vibrations is achieved by a remarkable combination of several symmetries intrinsic to the system: time reversal symmetry, the internal symmetries of the total angular momentum and the point symmetry of the local environment of the magnetic atom.

Restoring the Co Magnetic Moments at Interfacial Co-Porphyrin Arrays by Site-Selective Uptake of Iron

“…A partial electron transfer from the substrate via the d z 2-orbitals has to be included to achieve the above shown agreement, resulting in a new d 7 þd 8 ground state (with a total of 7.25 electrons). The finite mixing with the low spin d 8 -states with S = 0 forces singlet formation also in the d 7 configuration and results in a total quenching of the magnetic moment. The quenching of the spin moment follows the same arguments presented for CoPc on Au(111).…”

“…The quenching of the spin moment follows the same arguments presented for CoPc on Au(111). 56 Here, the Co ion assumes a d 7 In (c) and (d), the Ag background and a step function to compensate nonresonant absorption have been subtracted from the data. All X-ray absorption spectra have been normalized to the absorption intensity of the L 3 -edge maximum at θ = 0°.…”

“…This quenching is not unique for the C 4h symmetry. Further lowering the symmetry to C 2h , which occurs due to the saddle shape distortion of the molecules adsorbed on the surface, will modify slightly the energies of the ground state levels in the respective d 7 and d 8 configurations but will not further split the orbital A 1 singlets. Therefore, the same argument for spin quenching holds true also for lower symmetries.…”

Crystal field analysis of Dy and Tm implanted silicon for photonic and quantum technologies

“…The symmetry of the RE ion local environment is particularly important for RE quantum states, for example the magnetic moment of single neutral Ho atoms on a platinum substrate has been shown to have lifetimes of the order of minutes, which could be useful for the storage of qubits [19]. This long lifetime was explained because in the particular case of total angular momentum, J, = 8 for Ho and the C 3v symmetry of the Pt <111> substrate, the eigenstates of the crystal field Hamiltonian form three distinctive groups which can be used to show that the matrix elements describing a substrate electron-induced transition between degenerate m J magnetic sublevels vanish.…”

“…This means the Ho atoms are in effect invisible to the electrons moving through the Pt. Any RE atom with J = 3n + 1 or 3n + 2, for any interger n ≥ 0, should also show long lifetimes; this leaves only Pr and Pm, the later having no stable isotopes [19]. C 3v symmetry can occur for substitutional impurities in Si if there is distortion in the <111> direction, or if a pair of inequivalent substitutional atoms are bonded [20].…”