Quantum interference effects in molecular spin hybrids

We have studied by means of low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) single molecular spin hybrids formed upon chemisorbing a polycyclic aromatic, threefold symmetric hydrocarbon molecule on Co(111) nanoislands. The spin-dependent hybridization between the Co d states and the π orbitals of the molecule leads to a spin-imbalanced electronic structure of the chemisorbed organic molecule.

Spin-sensitive measurements reveal that the spin polarization shows intramolecular variations among the different aromatic rings in spite of the highly symmetric adsorption geometry promoted by symmetry matching of the threefold symmetric molecule and the sixfold symmetric Co(111) lattice. Hence the varying degree of spin polarization on the organic molecule does not stem from a different hybridization of the aromatic rings with the Co atoms, but is proposed to be a consequence of the superposition of the spin polarization of the molecule and the spatially modulated spin polarization of the spin-dependent quantum interference pattern of the Co(111) surface state.

In further studies it will be interesting to explore to what extent the spin properties of
hybrid molecular magnets can be modified by spin-dependent quantum interference patterns and to analyze the effect of the magnetic field on the hybrid molecular magnet in more detail to find out if the aromatic rings react differently on the magnetic field, e.g., if they switch at different magnetic fields.

Figure: (a) Constant-current STM image of a Co island with adsorbed TPT molecules (V = −200 mV and I = 200 pA). Note that the Co island is the same as in Fig. 9. (b) dI/dV map of the Co island with adsorbed TPT molecules at the energy of the hybrid state for antiparallel magnetization directions between tip and sample measured with a bulk Cr tip (V = −310 mV and I = 1.5 nA). Image section corresponds to the area indicated in (a). (c) As (b), but for the parallel state. (d) Spin asymmetry map calculated from the dI/dV maps in (b) and (c) according to Eq. (1) (see original publication). (e) and (f) The spin asymmetry map from (d) after applying a Gaussian filter to remove the noise. (f) For the purpose of illustration, the graphical representation of the TPT molecule has been overlaid to the map in (e). The positions of the TPT molecules have been extracted from the simultaneously recorded constant-current image.

Esat, Friedrich, Matthes, Caciuc, Atodiresei, Blügel, Bürgler, Tautz, Schneider
Quantum interference effects in molecular spin hybrid
Physical Review B 95(9) 094409 (2017)