Magnetic resonance on the single spin level

Single spin detection is one of the central challenges of nano science and technology. We have
developed an STM related technique for single spin magnetic resonance (ESR-STM). The importance
of such a technique is three-fold: chemical analysis on the nm or atomic scale; Single spin physics
(many of the new physical phenomena recently observed are spin related: High temperature
superconductivity; Dirac materials; topological insulators etc and quantum information and
computation using single spin qubits.)
We measure high frequency noise power densities in the STM tunneling current. When above a
single spin in an external magnetic field, it reveals peaks at the Larmor frequencies. This is done at
room temperature, and without spin polarized tunneling. In order to detect weak rf signals (of the order
of 1-3 pA) we use matching circuits, modulation techniques and sensitive detectors (spectrum
analyzers or rapid oscilloscopes).
ESR-STM measurements on different spin centers revealed g hyperfine and zero field splitting
tensors up to a single spin levels. This reveals information on the local environment of the single spin
– which is not detectable microscopically. We use the hyperfine levels for doing single spin double
resonance measurements to detect the nuclear transitions. The experiments are performed on magnetic
atoms, defects or molecules. Studies to extend the technique for non magnetic species by ionization are
in progress.
Current results have demonstrated the capability to detect a single spin hyperfine spectrum of one
Tempo molecule. When there is another molecule nearby, the dipolar interaction between the
molecules, modifies the spectrum and enables to calculate the distance between the two molecules.
The distance is in agreement with the STM image. This ability may have broad applications for
example in questions of molecular docking or in molecular magnets