Engineering Superposition States to Induce Atomic-Scale Spin Dynamics

Studying dynamical interactions between individual spins is vital to understanding exotic magnetic materials as well as for the development of applications that require control over solid state spins like spintronics and quantum computation. Here, we use the unique capability of the magnetic tip of a scanning tunneling microscope (STM) to tune the eigenstates of an atomic spin system into superposition states. This allows us to induce and control dynamics between the individual spins.

In a first series of experiments, we use a combination of electron spin resonance (ESR) and DC pump-probe techniques to induce a single spin flip and trace its superposition-induced dynamics through different atomic structures. Using careful positioning of the magnetic tip, we induce dynamics between two atoms [1], extended chains of atoms [2] and between the electron spin and nuclear spin within a single atom [3].

In a second series of experiments, we expand this technique towards dynamic control by oscillating the position of the magnetic tip, resulting in a periodic modulation of the magnetic eigenstates into and out of superposition. This gives us further control over the atomic spin states by driving Landau-Zener-type transitions in antiferromagnetic spin chains [4]. By using a Q-plus sensor to oscillate the magnetic tip, we even detect the magnetic dynamics of a single atom in the magnetic exchange force between tip and atom [5], opening the door to studying atomic spin dynamics without the need for a tunneling current.