1 IBM Almaden Research Center, San Jose, CA 95120, USA
2 Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, Korea
3 Department of Physics, Ewha Womans University, Seoul 03760, Korea
E-mail: willke.philip@qns.science

Abstract:
In this talk I will present our recent progress in single atom electron spin resonance (ESR) realized in a scanning tunneling microscope (STM) [1,2].
In the first part I will show that we can resolve and control the hyperfine interaction of individual atoms by using ESR-STM. Using atom manipulation to move single atoms we find that the hyperfine interaction strongly depends on the binding configuration of the atom as well as the proximity to other magnetic atoms. This allows the extraction of atom- and position-dependent information about the electronic ground state, the state mixing with neighboring atoms as well as properties of the nuclear spin. Thus, the hyperfine spectrum becomes a powerful probe of the chemical environment of individual atoms and nanostructures.
In addition, I show that we are able to extend ESR-STM to perform magnetic resonance imaging (MRI) for the first time on individual atoms. Here, we use the magnetic field of the STM tip to shift the Zeeman energy of the atom on the surface and cause spatial variations in the resonance frequency. While this is similar to existing scanning field gradient methods[3,4], our approach exceeds their spatial resolution by one to two orders of magnitude, to achieve Ångström resolution.
 Hyperfine interaction of individual titanium atoms. ESR spectra for 48Ti (top, nuclear spin I = 0) 47Ti (middle, I = 5/2) and 49Ti (bottom, I = 7/2). Right panel: STM images of the individual Ti atoms on a MgO surface.

REFERENCES:
[1] Baumann et al., Science 350, 6259 (2015).
[2] Willke et al., Science Advances 4, eaaq1543 (2018).
[3] Rugar et al., Nature 430, 329-332 (2004).
[4] Balasubramanian et al., Nature 455, 648 (2008).
Brief bio:
Philip Willke studies in Physics at University of Göttingen in Germany where he obtained his B.S. (2011), M.S. (2013) and Ph.D. (2017) degree. He became a postdoctoral researcher of IBS Center for Quantum Nanoscience in Seoul since 2017 and was awarded Feodor-Lynen research scholarship in 2018. His research interest focuses on exploring the nano world using scanning probe methods. This includes the magnetic and electronic properties of single atoms, atomic-scale defects and materials. He has investigated local electron transport as well as substitutional defects in graphene and is currently working on magnetic properties of single spin centers on surfaces. Accordingly, new tools and techniques need to be invented and developed, for instance he has further developed the scanning probe techniques of electron spin resonance combined with scanning tunneling microscopy (ESR-STM) as well as scanning tunneling potentiometry (STP).

报告联系人：李  更  博士
郇  庆  博士（82649096）