Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 60: [MA] Joint Session "Surface Magnetism II" (jointly with O)

O 60.7: Vortrag

Donnerstag, 29. März 2012, 11:00–11:15, EB 301

Probing individual spin states of Fe-Porphyrins on a superconductor — •Benjamin W. Heinrich, Lukas Z. Braun, José I. Pascual, and Katharina J. Franke — Institut für Experimentalphysik, Freie Universität Berlin, Germany

Scanning Tunneling Microscopy/Spectroscopy (STM/STS) allows for studying the competition between magnetism and superconductivity at a single-impurity level. Commonly, the adsorption of a magnetic atom [1,2], or molecule [3], on a superconductor locally breaks the time-reversal symmetry and gives rise to bound states in the superconducting (SC) gap [4], and/or Kondo quasi-particle states [3]. However, here we can show that decoupling the impurity spin from the SC substrate preserves both the local spin and the SC state.

We use inelastic electron tunneling spectroscopy (IETS) to probe the spin state of single Fe(III)-Octaethylporphyrin-Cloride (FeOEP-Cl) molecules adsorbed on Pb(111). Due to the bulky ligand, the interaction between the central Fe ion, holding the molecular spin, and the substrate is strongly reduced. At 4.5 K, we can observe spin flips on the molecule, while the SC quasi-particle resonances remain unchanged. Reducing the tip-sample distance allows for altering the local anisotropy, while desorbing the chlorine ligand via controlled voltage pulses results in a change of the spin state as revealed by energy shifts of the IETS signal.

[1] A. Yazdani et al., Science 275, 1767 (1997) [2] S.-H. Ji et al., Phys. Rev. Lett. 100, 226801 (2008) [3] K.J. Franke et al., Science 332, 940 (2011) [4] H. Shiba, Prog. Theor. Phys. 40, 435 (1968)