SFB 1238 | March 04, 13:30
From Correlated Electrons to Atomic-Scale Quantum Sensing
Scanning tunneling microscopy (STM) enables the fabrication and investigation of nanostructures with atomic precision and provides access to correlated electron phenomena as well as a route toward atomic-scale quantum devices. In this talk, I demonstrate how artificial molecular nanostructures serve both as model systems for Kondo correlations in the weak-coupling regime and as single-molecule quantum sensors. We fabricate these nanostructures by positioning planar aromatic molecules in an upright geometry on a pedestal of two metal atoms on a surface [1] or at the STM tip apex, where they host a well-isolated spin-1/2 that exhibits Kondo physics [2].
In the first part of the talk, I focus on the correlations and the Kondo scale of these structures on the surface. Performing tunneling spectroscopy at temperatures between 1 K and 30 mK in variable magnetic fields, and comparing the results with numerical renormalization group calculations, we show that the intrinsic Kondo scale lies 6-11 orders of magnitude below the experimental temperature. The results highlight the asymptotic freedom in the Kondo problem: the exchange coupling decreases only logarithmically at high energies, allowing Kondo signatures to persist far above the intrinsic Kondo scale.
In the second part, I demonstrate how the spatial resolution of quantum sensors can be advanced to the atomic length scale, which remains elusive for existing techniques. Using the same decoupling strategy, we fabricate a single-molecule quantum sensor at the STM tip. The weakly coupled spin-1/2 forms a two-level quantum system in a magnetic field that can be addressed by electron spin resonance (ESR), enabling the detection of magnetic and electric dipole fields from individual atoms with sub-angstrom spatial resolution [3].
[1] Esat, et al. Nature 558, 573-576 (2018).
[2] Esat, et al. Physical Review Research 5, 033200 (2023).
[3] Esat, et al. Nature Nanotechnology 19, 1466-1471 (2024).
Forschungszentrum Jülich
PH2
Contact: Erwann Bocquillon / Matteo Cacco