This section aims at helping you to have a visualized sense of how to perform an actual ESR measurement in STM. To make ESR spectroscopy easily understood, we start from a brief introduction of ESR detection mechanism, including tunneling magnetoresistance (TMR) effect, Larmor precession, heterodyne and homodyne detection, etc. Understanding the detection mechanism will help to extract useful information from the line shape of ESR spectra.
In order to perform a high-quality ESR measurement, a STM tip having good performance in spin polarization (sp) is of vital importance. In the corresponding modules, we focus on the tip influence on ESR measurements. We show a benchmarking recipe to prepare an sp-tip by transferring magnetic metal atoms from surface to tip apex and evaluate tip’s spin polarization by performing differential conductance (dI/dV) measurement. You can find several representative dI/dV spectra measured with our good sp-tips for reference. We also illustrate a ubiquitous physical model of the tip field which can be utilized as a controllable local magnetic field to address single spins. Based on this, a new ESR scheme – tip field-sweep has been developed and shows great potential compared to conventional frequency-sweep ESR measurements.
Additionally, we talk about the magnetic spin-spin interactions of metal atoms on surface and demonstrate how to study these interactions via precise ESR measurements. Finally, we access pulsed ESR field which is considered as one step ahead of normal continuous-wave ESR studies, from which coherent quantum control on single atom spins can be realized.