An ultimate goal of spintronic research is the realization of concepts for atomic-scale all-spin-based devices. We combined bottom-up atomic fabrication with spin-resolved scanning tunneling microscopy to construct and read out atomic-scale model systems performing logic operations. Our concept uses substrate-mediated indirect exchange coupling to achieve logical interconnection between individual atomic spins. Combined with spin frustration, this concept enables various logical operations between inputs, such as NOT and OR.

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We have performed single-atom magnetization curve (SAMC) measurements and inelastic scanning tunneling spectroscopy (ISTS) on individual Fe atoms on a Cu(111) surface. The SAMCs show a broad distribution of magnetic moments with 3.5 μB being the mean value. ISTS reveals a magnetization excitation with a lifetime of 200 fsec which decreases by a factor of 2 upon application of a magnetic field of 12 T. The experimental observations are quantitatively explained by the decay of the magnetization excitation into Stoner modes of the itinerant electron system as shown by newly developed theoretical modeling.

An individual magnetic atom doped into a semiconductor is a promising building block for bottom-up spintronic devices and quantum logic gates. Moreover, it provides a perfect model system for the atomic-scale investigation of fundamental effects such as magnetism in dilute magnetic semiconductors. However, dopants in semiconductors so far have not been studied by magnetically sensitive techniques with atomic resolution that correlate the atomic structure with the dopant's magnetism. Here we show electrical excitation and read-out of a spin associated with a single magnetic dopant in a semiconductor host. We use spin-resolved scanning tunnelling spectroscopy to measure the spin excitations and the magnetization curve of individual iron surface-dopants embedded within a two-dimensional electron gas confined to an indium antimonide (110) surface. The dopants act like isolated quantum spins the states of which are governed by a substantial magnetic anisotropy that forces the spin to lie in the surface plane. This result is corroborated by our first principles calculations. The demonstrated methodology opens new routes for the investigation of sample systems that are more widely studied in the field of spintronics-that is, Mn in GaAs (ref. 5), magnetic ions in semiconductor quantum dots, nitrogen-vacancy centres in diamond and phosphorus spins in silicon.

The time slice axiom states that the observables which can be measured within an arbitrarily small time interval suffice to predict all other observables. While well known for free field theories where the validity of the time slice axiom is an immediate consequence of the field equation it was not known whether it also holds in generic interacting theories, the only exception being certain superrenormalizable models in 2 dimensions. In this paper we prove that the time slice axiom holds at least for scalar field theories within formal renormalized perturbation theory.