Academic Affiliation: Synchrotron SOLEIL – L’orme des merisiers Saint-Aubin

Date and Time of the Talk: May 20th, 2021; 15:30 – 16:30

In the maze of the interaction between magnetic molecules and superconductivity

During the last decade, research on superconductivity found renewed interest since several theoretical works have announced the possibility to “fabricate” new topological phases by coupling superconducting solid-state systems with local magnetism and spin-orbit interaction [1]. Stabilization of such phases would be accompanied by the emergence of so-called Majorana edge states [2]. Experimental observation of such Majorana edge states would have a huge technological impact because they are considered good candidates for the realization of single qubits and their manipulation would provide a platform for the development of physical quantum computational systems.

To address this challenge, I focused on a hybrid system obtained by coupling self-assembled two-dimensional arrays of magnetic Metallo-organic molecules, i.e. manganese phthalocyanines (MnPcs), with thin films of lead (1 and 3 monolayers) grown on Si(111). In the first part of the talk, I will show the results [3] of the in-situ grown MnPcs/Pb/Si(111) system that has been characterized by Scanning TunnelingMicroscopy (STM) and spectroscopy (STS).

In the second part of the talk, I will focus on the results I obtained during the postdoc. One of the objectives of research in the field of organic spintronics is the understanding of the different paths through which localized spins in molecular lattices can interact to stabilize magnetic order, e.g. ferromagnetism or antiferromagnetism. In this regard, hybrid systems based on self-assembled layers of magnetic molecules, e.g.transition-metal phthalocyanines, supported by metallic substrates have been the subject of a huge number of studies [4,5]. When considering such organic/metal interface many types of coupling are at plays: in addition to direct exchange and superexchange coupling, so-called indirect exchange interactions that are mediated by the conduction electrons of the metallic substrate are also possible [6]. The interacting picture becomes dramatically more complicated if the substrate is allowed to be a superconductor. Magnetic atoms/molecules coupled to a superconductor induce bound states (Yu-Shiba-Rusinov(YSR) states [7]) within the superconducting gap. Under certain conditions, an overlap of YSR states associated to different magnetic atoms/molecules can mediate an indirect exchange interaction [8].

In order to explore and extract information about the magnetic signature of this mechanism, I carried out X-ray Magnetic circular dichroism (XMCD) experiments at 2K on different systems. In particular, I will present the results about (sub-) monolayers of MnPcs self-assembled on then on-superconducting HOPG and the superconducting 2H-NbSe2 [9].

References:

[1] Brauneckeret al., Phys. Rev. Lett. 111, 147202 (2013) / Hoffman S. et al., Phys. Rev. B92, 125422 (2015)
[2] SauJ.D. et al., Phys. Rev. B 82, 214509 (2010)
[3] D. Longo et al. J. Phys. Chem. C 36,19829 (2020)
[4] Wäckerlin C. et al., Chem. Commun. 51, 12958 (2015)
[5] Wu W. et al. , Phys. Rev. B 77, 184403 (2008)
[6] Wu W. et al. , Phys. Rev. B 77, 184403 (2008)
[7] Yu L., Acta Phys. Sin. 21, 75 (1965) / Shiba H., Prog. Theor. Phys. 40, 435 (1968) /Rusinov A.I., Sov. Phys. JETP Lett. 9, 85 (1969)
[8] Yao N.Y. et al. Phys. Rev. Lett. 113, 087202 (2014) / Hoffman S. etal., Phys. Rev. B 92, 125422 (2015) /Kezilebieke S. et al. Nano Lett. 2018, 18, 2311–2315 (2018)
[9] D.Longo et al., to be published