Chiral Materials Unlock Spin Polarization Without Magnetic Fields in Quantum Breakthrough

A new study has uncovered deeper connections between chirality and spin polarisation in materials. Researchers led by Johanna Erdmenger have explored how chiral structures can filter electron spins without magnetic fields. Their findings suggest fundamental quantum principles may govern this process, known as Chiral-Induced Spin Selectivity (CISS).

CISS occurs when electrons passing through chiral materials—such as certain molecules or magnets—develop a preferred spin orientation. Unlike traditional spin filters, this effect arises without external magnetic fields. The team, including René Meyer and Dmitri Vassilevich, examined theoretical frameworks like the chiral torsional anomaly and Nieh-Yan invariant to explain how geometry influences spin transport. Their work, published in arXiv:2409.08319 and JHEP, bridges quantum dynamics with observable spin currents.

At the University of Duisburg-Essen, separate research focused on chiral magnets like B20 FeGe. There, models incorporating the Dzyaloshinskii-Moriya interaction revealed how nonreciprocal spin waves and unidirectional anisotropy emerge. These studies highlight that spin precession frequency and electron dwell time within the chiral medium dictate CISS efficiency.

Further analysis showed that even light-element materials, which normally exhibit weak spin-orbit coupling, can display strong spin-dependent transport. Molecular chirality, electric fields, and structural distortions amplify effective spin-orbit interactions, enhancing polarisation. Machine learning and quantum simulations now help predict these behaviours across different chiral systems.

The researchers also proposed a multipole expansion formalism to unify various CISS manifestations. This approach clarifies how low-frequency vibrations in helical models can generate significant spin polarisation. Their findings suggest CISS is not static but evolves dynamically through coherent and dissipative interactions over time.

The studies provide a clearer picture of how chirality and spin interact at a quantum level. By linking theoretical models to experimental observations, the work opens pathways for designing spintronic devices without magnetic components. Future applications may benefit from these insights into spin filtering in chiral materials.