Seminar: Molecular spin coupling at the tip of an STM

By Laurent Limot
CNRS researcher at the IPCMS in Strasbourg

Wednesday 16 April 2018 at 10.30 a.m.
IEMN Boardroom - Villeneuve d'Ascq



Recent advances in addressing and controlling the spin states of a surface-supported object (atom or molecule) have further accredited the prospect of quantum computing and of an ultimate data-storage capacity [1]. Information encoding requires that the object must possess stable magnetic states, in particular magnetic anisotropy to yield distinct spin-dependent states in the absence of a magnetic field together with long magnetic relaxation times. Scanning probe techniques have shown that inelastic electron tunneling spectroscopy (IETS) within the junction of a scanning tunneling microscope (STM) is a good starting point to study the stability of these spin states [2]. STM-IETS allows for an all-electrical characterization of these states by promoting and detecting spin-flip excitations within the object of interest. As spin excitations need however to be preserved from scattering events with itinerant electrons, single objects are usually placed on non-metallic surfaces such as thin-insulating layers or superconductors. In this sense, new approaches to improve the detection of spin-flip excitations are desirable. With this purpose we present here a novel strategy based on the molecular functionalization of a STM tip. We study the surface magnetism of a simple doubledecker molecule, nickelocene [Ni(C5H5)2], which is adsorbed directly on a copper surface. By means of X-ray magnetic circular dichroism and density functional theory calculations, we show that nickelocene on the surface is magnetic (Spin = 1) and possesses a uniaxial magnetic anisotropy, while IETS reveals an exceptionally efficient spin-flip excitation occurring in the molecule [3]. Interestingly, nickelocene preserves its magnetic moment and magnetic anisotropy not only on the surface, but also in different metallic environments. Taking advantage of this robustness, we are able to functionalize the STM tip with a nickelocene [3,4], which can then be employed as a portable source of inelastic excitations. As we will show during the talk, IETS can then be used to probe the interaction between a surface-supported object and the nickelocene tip, including a magnetic interaction.

M. Ormaza1, P. Abufager2, B. Verlhac1, N. Bachellier1, M.-L. Bocquet3, N. Lorente4, and Laurent Limot1,*
1Université de Strasbourg, CNRS, IPCMS, UMR 7504, F-67000 Strasbourg, France
2Instituto de Física de Rosario, CONICET, Universidad Nacional de Rosario, Argentina
3Ecole Normale Supérieure, UPMC Univ. Paris 06, CNRS, 75005 Paris, France
4CFM/MPC and DIPC, 20018 Donostia-San Sebastián, Spain

[1] F.D. Natterer et al, Nature 543, 226 (2017); T. Choi et al, Nat. Nanotech. 6 (2017)
[2] A.J. Heinrich, J.A. Gupta, C.P. Lutz, and D.M. Eigler, Science 306, 466 (2004)
[3] M. Ormaza et al, Nano Lett. 17, 1877 (2017)
[4] M. Ormaza et al, Nat. Commun. 8, 1974 (2017)