When electrons pass through a molecule with a spiral structure - i.e., a chiral molecule, giant spin polarization is induced in the passing electrons. This phenomenon, called chirality-induced spin selectivity (CISS), is being actively researched worldwide.
This CISS effect is thought to involve a nontrivial coupling mechanism between electrons and spin that inherently exists within chiral structures. Although a large amount of supporting evidence has been reported, quantitatively evaluating this mechanism has been difficult, presenting a significant challenge in CISS research.
A research team led by Assistant Professor Takuro Sato, Graduate Student Hiroshi Goto, and Professor Hiroshi M. Yamamoto from the Research Center of Integrative Molecular Systems at the Institute for Molecular Science focused on organic superconductors with chiral symmetry and verified nonreciprocity closely related to spin-orbit coupling. As a result, they successfully observed giant nonreciprocal conduction in the superconducting state, far exceeding theoretical predictions.
The emergence of such giant responses in organic materials with very small spin-orbit coupling is particularly noteworthy as it is considered essential for nonreciprocal conduction. This suggests a nontrivial coupling between electron motion and spin induced by chirality, with the strength significantly exceeding the value predicted from spin-orbit interactions in conventional organic materials. The study also revealed that the observed giant nonreciprocal effect can be explained by assuming the formation of spin-triplet Cooper pairs induced by chirality.
This achievement is expected to provide guidelines for new superconducting devices and functional design centered on chirality as a distinctive structure. The group's findings were published in Physical Review Research.
(a) Schematics of nonreciprocal transports by fluctuating Cooper pairs.
(b) Observed amplitude of nonreciprocity in the chiral organic
superconductor in comparison with polar inorganic superconductors.
Provided by the Institute of Molecular Science
Journal Information
Publication: Physical Review Research
Title: Sturdy spin-momentum locking in a chiral organic superconductor
DOI: 10.1103/PhysRevResearch.7.023056
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