Four-Dimensional Probe of Electron Spin-Spin Coupling

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Non-Technical AbstractThis project provides new understanding into the interaction energy between two electron spins with precise control of the distance between them by a homemade microscope capable of resolving dimensions below a millionth of the width of a human hair. The quantitative data form the basis for understanding magnetic ordering and provide numerical results that can be used (instead of parameters) in the analysis of a broad range of magnetic phenomena. The combined experimental and theoretical research impacts the next generation of information storage devices and futuristic technologies based on the electron spin properties of new materials. This microscope provides images of the spatially dependent interaction between two spins and allows direct visualization of this interaction. The use of homemade instrument to make measurements previously not possible to gain new understanding provides valuable education and training of students. This project teaches the students how to solve difficult problems and endows them with skills that allow them to tackle seemingly unrelated and highly challenging problems in their future careers. A byproduct of this research contributes to the creation of a highly skilled workforce in a society with increasingly sophisticated technologies. Technical AbstractThe coupling between electron spins is central to the understanding of magnetic phenomena and forms the basis for a number of important effects in atoms, molecules, and condensed matter. For atoms and molecules with spin moments adsorbed on a solid surface and interacting with a nearby spin, the energy of coupling depends on the exchange interaction and the magnetic anisotropy. The electron spin-spin coupling can be probed in four dimensions (E,x,y,z) using the scanning tunneling microscope (STM), at 0.6 K and up to 9 Tesla magnetic field, by attaching a molecule with an electron spin to the tip and measure the coupling energy (E) at different locations (x,y,z) over a single magnetic atom or molecule adsorbed on the surface. The realization of the spin-tip requires the implementation of a novel synthetic method based on STM manipulation of single atoms and molecules. This project yields precise data that enable quantitative analysis by theoretical calculations. This synergy between experiment and theory leads to the validation of the theoretical framework in understanding magnetism at a level not previously attainable and further extends this project to new and unforeseen directions. Still, results of the spatial dependence of the spin-spin interaction may also deviate from the conventional expectation and thus require a new framework of thinking.