Electron Spin Precession STM

In many solid state quantum computing schemes, detection of single spins is a requirement for setting up the initial state of the computer, effectively manipulating its bits, or reading out the results after an operation. The ability to detect single spins in a material at or near the surface may also lead to atomic resolution chemical identification and to direct studies of interacting networks of spins. Currently there are single spin detection efforts underway in resonance force microscopy techniques, single electron tunneling devices, etc. In our work, we are exploring the possibility of using Scanning Tunneling Microscopy to detect the spin of an atom or unpaired electron at the surface by the high frequency signal it is expected to induce in the tunneling current when placed in a static magnetic field.

The idea of detecting spin this way was first developed and experimentally demonstrated by Y. Manassen, et.al., in 1989 (Phys. Rev. Lett. 62, 2531). In that paper and others in the following years, Manassen showed evidence for a high frequency signal, at the same frequency as the expected Larmor precession, in STM data taken in a magnetic field. While the experimental results appear to be clear, their interpretation and understanding, and consequently further development and application of the technique, have not been forthcoming. A variety of theoretical papers have sought to explain or discount the experiments, but there are still no conclusive results concerning the origin or magnitude of the signal.

In our work, we are exploring the detection of single spins in a static magnetic field, via STM, by looking for the signal in "cleaner" spin systems than have been previously studied. We will also be carrying out temperature dependent and more detailed field dependent studies of these and the iron/silicon system studied by Manassen. Reproducing his results will be an important aspect of our work.

In support of this work we are also teaming directly with theorists Gennady Berman, Alexander Balatsky, and Ivar Martin at LANL to attempt to give the technique a solid understanding as well as suggest other useful experimental systems and measurements. Berman and coworkers are focussing on the physics of spin detection and manipulation and decoherence. Balatsky and Martin are developing a theory of the mechanism underlying the production of the STM signal. This work has already resulted in publications and has led us to rename the technique "electron spin precession scanning tunneling microscopy" (ESP-STM) since the Larmor precession of the spin is expected to be responsible for the high frequency tunnel current signal. (Originally this was called electron spin resonance (ESR) STM. ESR connotes experiments in which the spin frequency resonates with an applied RF field – only a static magnetic field is expected to be necessary for this technique.)