Research Unveils Chirality's Role in Electron Spin

Abstract

The interaction between electron spin and molecular chirality plays a fundamental role in quantum phenomena with significant implications for spintronics and quantum computing. The chirality-induced spin selectivity (CISS) effect, where chiral materials preferentially transmit electrons of a particular spin, has sparked intense interest and debate regarding its underlying mechanism. Despite extensive research, the spatial distribution of spin polarization in chiral systems, the key evidence to reveal the spin scattering mechanism in CISS, has remained experimentally elusive, particularly due to complications arising from spin-orbit coupling in metal electrodes typically used in such studies. Here we show, through reflective magnetic circular dichroism measurements on chiral tellurium nanowires with graphene electrodes, that current-induced spin polarization exhibits identical signs in both the nanowire and the electrodes, distinct from the presumed spin filter scenario. The observed spin polarization scales linearly with current amplitude, aligns parallel to the current direction, reverses with chirality or current flow, and demonstrates spin relaxation lengths of several micrometers into graphene. Our findings provide direct visualization of spatial spin distribution in chiral devices. This work demonstrates an approach for investigating spin-dependent phenomena in chiral materials and explores their potential impact for developing chirality-based spintronic and quantum devices.

The phenomenon where electron spins align in a specific direction after passing through chiral materials is a cornerstone for future spin-based electronics. Yet, the precise process behind this effect has remained a mystery-until now. An international team of researchers, affiliated with UNIST has directly observed how electron spins behave in real space, providing fresh understanding of this complex interaction.

Professors Noejung Park and Seon Namgung from the Department of Physics at UNIST, in collaboration with Professor Binghai Yan from Pennsylvania State University conducted the study. Their work confirms that chiral materials actively change the spin orientation of electrons, overturning the long-held belief that these materials simply filter spins without affecting their direction.

Chirality, much like how left and right hands are mirror images but not identical, is a property found in many natural structures, including DNA and helical springs. When an electric current runs through such structures, electrons with a certain spin tend to pass through more easily-a key principle that could drive the development of advanced spintronic devices.

However, how exactly this happens has been debated. The main theories have been either that chiral materials act as spin filters-blocking one spin orientation and letting the other pass-or that they actively realign the electron's spin based on their structure.

To clarify this, the team conducted experiments using tellurium nanowires, which have a naturally helical shape. They connected these nanowires to graphene electrodes and used specialized microscopy to observe the spins directly.

The results were striking, as the spin directions in the nanowire and the electrodes matched perfectly. If the material were just filtering spins, you'd expect the reflected and transmitted spins to have opposite signs. Instead, the same spin orientation persisted, strongly supporting the idea that chiral structures actively manipulate electron spins.

In addition, theoretical calculations showed that as electrons pass through the chiral material, they acquire orbital angular momentum aligned with the structure's handedness, which then determines their spin direction.

Professor Namgung commented, "Seeing this behavior directly confirms how spins behave in chiral materials. It opens up exciting possibilities for designing new spintronic and quantum devices based on chirality."

The findings of this research have been published in ACS Nano on December 23, 2025. This study has been supported by funding from the Ministry of Science and ICT (MSIT) and the National Research Foundation of Korea (NRF).

Journal Reference

Jaehyun Lee, Sang-Hyuk Lee, Uiseok Jeong, et al., "Real Space Imaging of Spin Scattering in Chirality-Induced Spin Selectivity," (2025).