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Quenching of magnetic excitations in single adsorbates at surfaces: Mn on CuN/Cu(100)

The lifetimes of spin excitations of Mn adsorbates on CuN/Cu(100) are computed from first-principles. The theory is based on a strong-coupling T-matrix approach that evaluates the decay of a spin excitation due to electron-hole pair creation. Using a previously developed theory [Phys. Rev. Lett. {\bf 103}, 176601 (2009) and Phys. Rev. B {\bf 81}, 165423 (2010)], we compute the excitation rates by a tunneling current for all the Mn spin states. A rate equation approach permits us to simulate the experimental results by Loth and co-workers [Nat. Phys. {\bf 6}, 340 (2010)] for large tunnelling currents, taking into account the finite population of excited states. Our simulations give us insight into the spin dynamics, in particular in the way polarized electrons can reveal the existence of an excited state population. In addition, it reveals that the excitation process occurs in a way very different from the deexcitation one. Indeed, while excitation by tunnelling electrons proceeds via the s and p electrons of the adsorbate, deexcitation mainly involves the d electrons.