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New Attempts to Take Advantage of Magnets to Separate Handedness

As far as multiple research fields are concerned, chirality control of crystals and molecules is crucial.

The handedness of a spiral structure is inverted by taking the mirror image. A spin chirality, represented by an antiparallel-spin pair, is inverted not only by taking the mirror image but also by running time backward, which is not the case with a spiral structure. Such a spin chirality was shown to be connected to a structural chirality by measurements on a chiral superconductor under alternating current excitation. image Credit: Hiroshi Yamamoto, Institute for Molecular Science.

Recently, many attempts have been made to take advantage of magnets to isolate the handedness (left or right) of chiral molecules from chemical methods in a new fashion.

However, the suggested mechanism of the new approach has been debatable from the perspective of physics. The basic hypothesis remains to be confirmed, which is worth addressing for greater efficiency and more extensive coverage of magnet-based chirality control.

To test the hypothesis, you must map electron spins in a single chiral molecule. A big difficulty is that chiral molecules are so small that you cannot do so. Instead, we took up an organic chiral superconductor as a giant chiral molecule.

Hiroshi Yamamoto, Team Leader and Professor, National Institutes of Natural Sciences

Electrons need to be correlated or interfere with each other to stabilize electron spins through the full system. In a superconducting state, the interference continues through the extended coherence of electrons.

Several electrons collapse into a single quantum-mechanical wave and together retain the interference capacity through a long distance. This feature might allow emulation of the spin distribution present in an organic chiral superconductor in a much bigger length scale compared to the chiral molecules.

Through a combination of latest techniques, we finally detected spin polarizations. We are surprised by an excellent correspondence with the proposed hypothesis. We found different spin distributions for different handedness of chiral superconductors.

Ryota Nakajima, Study Leading Author and PhD Candidate, National Institutes of Natural Sciences

The observed spin distribution is relevant to chiral recognition. Depending on the handedness, two spin polarizations sit face-to-face or back-to-back at both edges of a superconductor. This unique configuration has been hypothesized for chiral molecules, but it has not been verified,” explains Assistant Professor Daichi Hirobe, one of the two corresponding authors.

Such spin configuration is unaltered in any rotation of a chiral crystal structure, which is important to magnet-based chiral recognition in a liquid reported earlier.

Professor Hiroshi Yamamoto notices the team's achievement as a big progress in comprehending a sensitive connection between magnetism and chirality.

Chirality made from spin distributions enables a recognition of molecular/crystal chirality from outside the system. This appears to defy the law of physics without careful consideration.

Hiroshi Yamamoto, Team Leader and Professor, National Institutes of Natural Sciences

The research group coined “T-odd chirality” for spin-related chirality, noting that the spins are reversed by the time-reversal operation “T.” Moreover, their finding is anticipated to identify applications in superconducting spintronics in the future.

Journal Reference:

Nakajima, R., et al. (2023) Giant spin polarization and a pair of antiparallel spins in a chiral superconductor. Nature. doi.org/10.1038/s41586-022-05589-x.

Source: https://www.nins.jp/en/

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