Characterizing the interaction of magnetic molecules with superconductors

Orateur : Nino HATTER (FU Berlin)

Almost 60 years after the explanation of conventional superconductivity by the BCS theory [1], research interest in the field of superconductors is still unbroken. For example, magnetic adsorbates on a type-I superconductor create a scattering potential for the quasi-particles of the superconductor. This leads to so-called Yu-Shiba-Rusinov [2,3,4] (Shiba) states inside the superconducting gap as well as a Kondo resonance outside the gap. The sensitive interplay of these two processes is governed by the exchange interaction of the impurity spin with the substrate quasiparticles. In this talk, I will focus on manganese-phthalocyanine (MnPc) molecules on the type-I superconductor Pb(111). We study this system by scanning tunneling microscopy. At 1.2 K we resolve triplets of Shiba resonances. A multitude of different adsorption sites provides access to a large range of magnetic coupling strengths with the substrate, which we use to identify the origin of the multiplets. We resolve the splitting of the Shiba states throughout the quantum phase transition from the "Kondo screened" to the "free spin" ground state and can link the splitting to the presence of magnetic anisotropy in the molecule-substrate system. Furthermore, the change in intensities of the Shiba resonances allows the unambiguous determination of the many-body ground and excited states [5]. I will also discuss preliminary results on the effects of adsorbed ammonia on MnPc and how this affects the coupling of the impurity spin to the substrate. There, we find a systematic modification of the Shiba bound states implying a decoupling of the system from the substrate. Additionally, a split Kondo resonance at very low magnetic fields is seen, which can help to understand in detail the role of the magnetic interaction governing the present system.

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