137th CEMS Colloquium

Title

Chirality and electron spin

Abstract

Chirality-Induced Spin Selectivity (CISS) is attracting recent attention as a new source of spin polarized current. It also provides unique methods for enantio-separation [1], enantio-selective electrochemical reactions, and efficient water oxidation. The mechanism of CISS effect is, however, yet to be clarified, as the effect is much larger than expected one estimated with small spin-orbit coupling for organic molecules. In a hypothetical consideration, it is proposed that an enhancement of spin polarization is associated with anti-parallel spin pair at two opposite ends of a chiral molecule [1]. It is interesting to note that such an anti-parallel spin pair is a time-reversal (T) odd state, while the chiral molecular structure is T-even. We think symmetry conversion from T-even to T-odd quantities gives an essential clue to understand CISS effect that can generate huge spin polarization in a non-equilibrium condition.

We have made such a symmetrical consideration based on multipole basis and found that a T-odd chirality can emerge from an accumulation of spin current [2]. In a chiral metal, we have confirmed that the CISS effect appears as spin polarization [3] rather than spin filtering. In addition, we have shown that chiral organic superconductors can exhibit spin accumulation at two opposite crystal edges whose directions are anti-parallel to one another [4]. This can be regarded as a macroscopic-size emulation of chiral molecules that has T-odd spin pairs at their opposite ends. It is interesting to note that gigantic non-reciprocal conductivity is also observed for the same system [5]. A connection to falsely chiral influence [6] will be also discussed.

References
1) K. Banerjee-Ghosh et al., Science 360, 1331 (2018)
2) J. Kishine, H. Kusunose, and HMY, Isr. J. Chem. 62, e202200049 (2022)
3) Y. Nabei, HMY et al., Appl. Phys. Lett. 117, 052408 (2020)
4) R. Nakajima, HMY et al., Nature 613, 479 (2023)
5) T. Sato, HMY et al., Phys. Rev. Res. 7, 023056 (2025)
6) L. D. Barron Chem. Soc. Rev. 15, 189 (1986)

Contact

email: yasano@riken.jp
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