Lifetime enhancement of an atomic spin chain near a diabolic point

Body The magnetic lifetime of bistable atomic nanostructures at very low temperatures is governed by quantum tunnelling of magnetization. Here we demonstrate experimentally that this process can be reduced several orders of magnitude by tuning the system close to a so-called diabolic point, resulting in dramatically longer lifetimes. We use a scanning tunnelling microscope with a spin-polarized tip to probe the lifetime of chains of Fe atoms on Cu2N/Cu(100) while applying a strong transverse magnetic field. Unlike other lifetime enhancing factors, such as a longitudinal field, chain length, bias voltage and current strength, the effect of the transverse field is non-monotonic with a pronounced peak around 3-4T. We explain this result through a reduction in the hybridization of the two lowest eigenstates, which exhibit an avoided level crossing in the vicinity of a diabolic point. While the avoided crossing is nearly indistinguishable, the peak in the lifetime is very clear, has a peak width that relates to the energy difference and is robust to variations in the experimental conditions. Using this method, it is shown that there is a significant variation in the g-factors of the individual atoms in the chain that is not symmetric along the chain. The work provides prospects for optimizing spintronic lifetimes through engineering of quantum states.