Daniel Wegner, Institute for Molecules and Materials, Radboud University Nijmegen, the Netherlands

Spin-Orbit Coupling on Surfaces and in Molecules: from Rashba to OLEDs to Molecular Magnets

I will present an overview of our recent STM/STS activities on systems where spin-orbit coupling plays an important role:

1. The well-known Bi/Cu(111) surface alloy exhibits several Rashba-split surface states. Through spectroscopic mapping of electronic standing waves, various intra- and interband scattering channels can be detected. A simultaneous analysis permits a full recovery of the surface band structure including the Rashba splitting [1]. In the unoccupied region, we find deviations from a simple picture of allowed and forbidden scattering channels.

2. State-of-the-art OLED devices are based on phosphorescent molecules ("triplet emitters"). The strong spin-orbit coupling of these heavy-metal complexes can reach light-conversion efficiencies up to 100% compared to only 25% for purely organic fluorescent molecules. I will present STM and STS results of a new class of square-planar Pt-based triplet emitters that show interesting modified properties at the organic-metal interface that may allow for new, dramatically simplified OLED architectures [2].

3. I will present our strategy and first results of synthesizing single-molecule magnets (SMMs) on surfaces in an atom-by-atom fashion via STM manipulation. Utilizing molecule-substrate coupling as well as organic-metal bonding, we can tune the molecular conformation of the octagonal carbon ring cyclooctatetraene [3]. This molecule is a building block for rare-earth metallocene-type molecular magnets, and our results pave a route toward building them in a bottom-up fashion.

References:

[1]    M. Steinbrecher et al., Phys. Rev. B 87, 245436 (2013).

[2]    P. R. Ewen et al., Phys. Rev. Lett. 111, 267401 (2013).

[3]    H. Harutyunyan et al., Chem. Commun. 49, 5993 (2013).

Host: Professor Philip Hofmann, iNANO & Department of Physics and Astronomy