On-line SPICE-SPIN+X Seminars
On-line Seminar: 13.01.2021 - 15:00 German Time
Chirality Induced Spin Selectivity: Open questions and challenges
Bart van Wees, University of Groningen
The phenomenon of chirality induced spin selectivity (CISS) has been known for over two decades . A strong coupling between spin and charge transport has been observed, which depends on the chirality (or helicity) of the molecules. These systems are non-magnetic, so the origin of CISS must lay in manifestations of the spin-orbit interaction between moving electrons and the chirality induced electric fields present in the chiral systems.
In this talk I will give an overview of the manifestations of chirality in nature, as well as the experimental status of CISS in electronic and spintronic transport experiments. In particular I focus on experiments where CISS is observed as a spin-valve magneto resistance (MR) in two-terminal devices, where a ferromagnet is used to polarize or analyze the spins transmitted through the chiral systems. I will discuss our recent theory work, where we emphasize the important symmetry differences between the spin-charge coupling in ferromagnets, which breaks time reversal symmetry, and in (non-magnetic) chiral systems, which preserves time reversal symmetry. This prohibits the observation of CISS induced MR in two-terminal systems (but still allows it in multiterminal devices). Experiments on CISS also explore the non-linear transport regime, where voltage biases are employed which exceed the thermal energy. In this regime a CISS induced MR is possible. However, its sign depends not only on the chirality, but also on the nature of the transport through the ferromagnet and chiral system.
Finally I will discuss a possible connection between the absence/presence of CISS induced MR in electronic transport measurements with experiments which demonstrated magnetization/magnetic field self-assembly of chiral molecules. .
 K. Ray, S.P. Ananthavel, D.H. Waldeck, R. Naaman, Asymmetric scattering of Polarized electrons by organized organic films made of chiral molecules, Science, 283, 814 (1999).
 X. Yang, C.H. van der Wal, and B.J. van Wees, Spin-dependent electron transmission model for chiral molecules in mesoscopic devices, Phys. Rev. B 99, 024418 (2019)
 X. Yang, C. H. van der Wal, and B. J. van Wees, Detecting Chirality in Two-Terminal Electronic Nanodevices, Nano Lett. 20, 8, 6148–6154 (2020)
 K. Banerjee Kosh et al., Separation of enantiomers by their enantiospecific interaction with achiral magnetic substrates, Science 10 May (2018)