Mechanism of electron-spin resonance studied with use of scanning tunneling microscopy

The observation of the precession frequencies of individual paramagnetic spins with use of scanning tunneling microscopy is explained here by a spin-orbit-coupling mechanism. Excitation of the paramagnetic dangling bond into a superposition of states will lead to charge-density oscillations, which add a time-dependent term to the tunneling barrier. The nonlinear dependence of the tunneling current on the barrier shape will give rise to a Larmor frequency component in the tunneling current. It is shown how the signal should be affected by different parameters, such as the relative orientations between the tunneling electrons and the dangling bond or the initial spin excitation. Possibilities that will be opened with this technique, as well as the questions that will have to be resolved, are discussed.