Electron Spin Flip with the STM, Ferromagnetic Resonance with XMCD

When an electron is placed into a magnetic field oriented along the z-axis, the spin up and down states split up by the Zeemann energy. Recent work suggests that the noise spectrum of the tunnel current recorded with an STM above unpaired spins contains a peak at the according frequency. However, the experiments are challenging, since this signal is weak and situated in the RF region, requiring high frequency detection of the tunnel current. In a collaboration with Dr. G. Boero of the group of Prof. R. Popovic in micro-technical engineering at EPFL, we are currently attempting to record the peak as a function of DC field and tip-sample distance above surface adsorbed molecules with radicals. If this approach is feasible, one of the ideas is to use molecules with known g-factor of their radical as probe for the local magnetic field, for instance created by a magnetic nanostructure. In the literature this technique has been called electron spin resonance (ESR) STM, we prefer to call it electron spin flip STM (ESF-STM) since at present we do not intend to apply additional AC-fields as in ESR.