Abstract
We investigate the spectral evolution in different metal phthalocyanine molecules on NbSe2 surface using scanning tunnelling microscopy (STM) as a function of the coupling with the substrate. For manganese phthalocyanine (MnPc), we demonstrate a smooth spectral crossover from Yu-Shiba-Rusinov (YSR) bound states to spin-flip excitations. This has not been observed previously and it is in contrast to simple theoretical expectations. We corroborate the experimental findings using numerical renormalization group calculations. Our results provide fundamental new insight on the behavior of atomic scale magnetic/SC hybrid systems, which is important, for example, for engineered topological superconductors and spin logic devices.
Highlights
P recise control of the properties of magnetic impurities on surfaces, such as the spin state and magnetic anisotropy, is one of the ultimate goals in fabricating atomic or molecular scale devices for data storage or computing purposes
The bound state results from the spindependent scattering of Bogoliubov quasiparticles on the impurity and is associated with the longitudinal part of the exchange interaction, JSzsz, where s represents the spin-density of the substrate electrons at the impurity position
Adsorption site of the magnetic impurity,[22] they have not been observed simultaneously in a single configuration. This suggests that the complete picture of the interplay between these two effects is more complicated, requiring a full manybody treatment of the quantum mechanical spin degree of freedom interacting with a continuum of electrons
Summary
Adsorption site of the magnetic impurity,[22] they have not been observed simultaneously in a single configuration. On FePc (Figure 3c), the two spin excitation energies monotonously increase with decreasing tip−sample distance These variations in the YSR and spin excitations states of the MPc molecules are caused by the interaction of the STM tip causing the metal ion to be pulled toward the STM tip.[31,32,51] This has the largest effect on the out-of-plane d-orbitals (dxz/yz and dz2), where the overlap with the substrate wave function will be strongly affected. We can plot the renormalized (effective) magnetic anisotropy Deff and the intensity of the spin-flip transitions as a function of the estimated ρJ (Figures 4d,e) This is possible as the energy of the YSR state depends only very weakly on the precise value of D in the experimentally relevant range (SI Figure S8).
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