Spin decoherence of magnetic atoms on surfaces

Abstract

We review the problem of spin decoherence of magnetic atoms deposited on a surface. Recent breakthroughs in scanning tunnelling microscopy (STM) make it possible to probe the spin dynamics of individual atoms, either isolated or integrated in nanoengineered spin structures. Transport pump and probe techniques with spin polarized tips permit measuring the spin relaxation time $T_1$, while novel demonstration of electrically driven STM single spin resonance has provided a direct measurement of the spin decoherence time $T_2$ of an individual magnetic adatom. Here we address the problem of spin decoherence from the theoretical point of view. First we provide a short general overview of decoherence in open quantum systems and we discuss with some detail ambiguities that arise in the case of degenerate spectra, relevant for magnetic atoms. Second, we address the physical mechanisms that allows probing the spin coherence of magnetic atoms on surfaces. Third, we discuss the main spin decoherence mechanisms at work on a surface, most notably, Kondo interaction, but also spin-phonon coupling and dephasing by Johnson noise. Finally, we propose some schemes to engineer spin decoherence.

60 pages, 6 figures

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• Tuning paramagnetic spin-excitations of single adatoms
• General scheme for stable single and multiatom nanomagnets according to symmetry selection rules
• Relaxation and decoherence of qubits encoded in collective states of engineered magnetic structures
• Decoherence and pointer states in small antiferromagnets: A benchmark test
• Spin-1 two-impurity Kondo problem on a lattice
• Transport properties of Co in Cu(100) from first principles