From Inelastic Tunneling Spectroscopy to Electron Spin Resonance of single atom spins on a surface*

The scanning tunneling microscope is an amazing tool because of its atomic-scale spatial resolution. This can be combined with the use of low temperatures, culminating in precise atom manipulation and spectroscopy with microvolt energy resolution. In this talk I will apply these techniques to the investigation of the quantum spin properties of transition metal atoms on surfaces and will focus on some of the technical aspects of these techniques.
In the first part we will describe the development of a STM that operates in vacuum at temperatures below 1K and in high magnetic fields. That tool allowed us to measure the small energy required to flip a spin in an inelastic electron tunneling spectroscopy which we called spin excitation spectroscopy. In addition to the Zeeman energy, this technique can be used to measure single-atom magnetic anisotropy as well as spin-spin coupling in dimers and chains.
In the second part we will describe the experimental advances that were required to measure fast spin relaxation processes in an STM by all-electrical means. In this technique, short voltage pulses are applied to the STM tunnel junction and a pump-probe measurement scheme with variable delay time gives time resolution of about 1 nanosecond.
We will conclude with our recent measurements of electron spin resonance in an STM. This approach requires Gigahertz frequency electric fields in the tunnel junction which coherently drive a spin resonance in the spin states. It offers unprecedented energy resolution on the atomic scale, about 10,000 times better than typical low-temperature STM spectroscopy.