Tag Archive for: Seminar

Seminar: Molecular spin coupling at the tip of an STM

By Laurent Limot
CNRS researcher at the IPCMS in Strasbourg
Contact: limot@ipcms.unistra.fr

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

 

Abstract:

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

References
[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)

 

 

Seminar: About non-regular dynamics

By Alain Léger
Director of Research at the CNRS
Contact: leger@lma.cnrs-mrs.fr

Wednesday 28 March 2018 at 14:00
IEMN Ampli LCI - Villeneuve d'Ascq

Abstract:

This talk will present some aspects, first introductory, then more recent, of non-regular mechanics. A number of situations, edge conditions or behaviour laws provide examples of non-regularity in mechanics. We will concentrate mainly on the case of contact and friction, but several fundamental aspects would be identical in the cases of plasticity, damage, etc. In all cases, the introduction of non-regular conditions in continuum mechanics leads to open and difficult mathematical problems. To this end, an attempt will be made to give a detailed account of the current state of affairs, in the form of a list of problems that have been solved or are still open, so as to clarify the situations in which it is legitimate or not to use results from different areas of physics, and it will be observed that it is in these cases simple models which, provided they are well chosen, provide qualitative information where models closer to physics would be inaccessible.

It will be recalled that non-regularity removes the possibility of referring to the classical framework of the theory of differential equations or partial derivatives. After a few results, stated in the case of a very simple mechanical system but generalisable to all discrete problems, a large part of the presentation will be devoted to the study of the response to a periodic load, as is traditional in the qualitative study of dynamic systems.

Initially, the mechanical system will be linear, which will make the results usable qualitatively in many areas of physics, acoustics or vibrations. Particular attention will be paid to the transition between zones of different behaviour, and it should be noted that no transition to chaos is observed when the only non-linearity is due to contact and friction. We will then add a regular non-linearity of the large deformation type. We will then see that the response can include zones of non-periodic behaviour, which will lead us to question the coupling between different types of non-linearity.