Academic Affiliation: Research Center Jülich, Germany

Research Area: Understing fundamental properties on the nanoscale with the focus on magnetic excitations and correlated systems.

Research stay period: February 09 – 22, 2020

Talk: February 11, 16:00 – 17:00

Sensing dark spins with a scanning tunneling microscope

Probing the spin of individual atoms and molecules on surfaces by means of inelastic electron tunneling spectroscopy (IETS) has since its introduction [1] developed to a very successful and widely used method in scanning tunneling microscopy [2]. Recently, IETS measurements have been also taken simultaneously on two magnetic impurities, one attached to the apex at the tip, the other one on the sample surface, revealing correlation-driven transport asymmetries, reminiscent of spinpolarized transport in a magnetic field [3]. In this experiment only the spin on the surface was spectroscopically active while the one on the tip was spectroscopically dark.

Here now I will show how the transport is significantly altered when the tunneling electron is interacting with both spins simultaneously; the one on sample and the one on the tip apex. Different to measurements on two S = 1spins which only showed the expected steps in the differential conductance at each individual excitation and the sum of both excitations [4] we observe complex IETS data when we use a functionalized tip apex with a high S = 3/2 Kondo system to probe a S = 2 Fe adatom on the CuN surface. To successfully simulate such spectrum, Kondo as well as potential scattering processes have to be taken into account whereby strong interference effects due to the fermionic nature of the tunneling electrons lead to novel selection rules [5].

The understanding of the transport rules is important because it enables one to use well understood surface supported spins to calibrate the spin at the ill defined tip apex. Successively, such spin can then be used as a well characterized mobile sensor with unprecedented spacial resolution [6].

References:
[1] A.J. Heinrich, J.A. Gupta, C.P. Lutz, and D.M. Eigler, Science 306, 466 (2004).
[2] M. Ternes, New J. Phys. 17, 063016 (2015).
[3] M. Muenks, P. Jacobson, M. Ternes, and K. Kern, Nature Comm. 8, 14119 (2017).
[4] M. Ormaza, et al., Nano Lett. 17, 1877 (2017).
[5] M. Ternes, C.P. Lutz, A.J. Heinrich, and W.-D. Schneider, arXiv:1908.08267 [cond-mat.meshall].
[6] B. Verlhac, et al., Science 366, 623 (2019).