Abstract

The spin dynamics of electrons in chiral molecular systems remains a topic of intense interest, particularly regarding whether geometric chirality inherently induces spin polarization in current-carrying electrons. In this work, we employ ab initio real-time time-dependent density functional theory (rt-TDDFT) to directly simulate the interplay among charge current, spin, and orbital. This real-time tracking extends beyond perturbative treatments, and we analyze how nonequilibrium currents effectively lift the symmetry constraints of screw rotation and time-reversal symmetry. We find that the emergence of spin and orbital angular momenta is dynamically correlated with a concomitant loss of translational (linear) momentum, which we interpret as an intrinsic consequence of current-driven symmetry lowering. The implications of this mechanism for chirality-induced spin selectivity and spintronics device design are discussed.

A new theoretical study shows that simply passing an electric current through chiral, helical materials can generate the intrinsic spin of electrons. Using real-time quantum calculations, researchers tracked how electron motion transforms into spin and orbital angular momentum.

Led by Professor Noejung Park from the Department of Physics at UNIST, the team partnered with scientists from the University of Missouri, Pennsylvania State University, and the Max Planck Institute. They simulated electrons flowing through a one-dimensional helical conductor—specifically selenium nanowires—and uncovered the microscopic process behind spin polarization.

Electrons carry two types of angular momentum: spin and orbital. Under normal conditions, these cancel out. But in chiral structures, an electric current favors electrons with a specific spin, creating a phenomenon known as chirality-induced spin selectivity (CISS). This effect enables spin control without magnetic fields, promising for spintronic devices. Yet, how current drives this spin polarization remained unclear.

The simulations revealed that as electrons move along the helix, their linear momentum converts into orbital angular momentum. This transfer, driven by the current, couples with the electron’s spin via quantum spin-orbit interaction, leading to a net spin polarization. Notably, this process activates only above a certain current threshold and persists even after the electric field is turned off.

Professor Park explains, “Our work shows that the flow of current itself creates and sustains spin polarization in chiral conductors. It highlights a fundamental mechanism—orbital angular momentum transfer—that can be harnessed for next-generation spintronic devices operating purely on electrical signals.”

The findings were published in ACS Nano on April 23, 2026. The study has been supported by the National Research Foundation of Korea (NRF) grants funded by the Ministry of Science and ICT (MSIT), and by a KIAT grant funded by the Ministry of Trade, Industry, and Energy (MOTIE).

Journal Reference

Uiseok Jeong, Daniel Hill, Esmaeil Taghizadeh Sisakht, et al., "Current-Driven Symmetry Breaking and Spin–Orbit Polarization in Chiral Wires," ACS Nano, (2026).