Abstract

Quantized charge pumping in one-dimensional chiral wires has been widely studied in the context of topological physics in (1 + 1)-dimensional synthetic space, yet the role of orbital and spin degrees of freedom remains largely unexplored. Here, we show that topological charge pumping in insulating chiral systems intrinsically generates orbital and spin polarization, providing a new perspective on spin-selective transport in chiral materials, often associated with chirality-induced spin selectivity. Using time-dependent Schrödinger dynamics of multiorbital tight-binding models driven by circularly polarized light, we identify two key results. First, the screw-like geometry enables a single-parameter topological charge pumping. Second, while the energy gap remains open throughout the pumping cycle, Berry phase driven dynamics induces nonequilibrium orbital polarization. Through spin–orbit coupling, this orbital response is partially converted into spin polarization. By analogy between synthetic (1 + 1)- and two-dimensional topological insulators, we suggest that nontrivial spin–orbital dynamics may accompany anomalous quantum charge Hall states. 

A new theoretical study has demonstrated that a spiral-shaped nanowire can function as a quantum pump—transferring electrons in precise, quantized amounts. This discovery reveals a novel approach to controlling charge flow at the nanoscale, grounded in the topological properties of the material.

Led by Professor Noejung Park of the Department of Physics at UNIST, in collaboration with researchers at Pennsylvania State University, the team shows that a one-dimensional, screw-like chiral material can generate a topological charge pump. During this process, the system also produces orbital angular momentum and spin polarization, unveiling new connections between topology and quantum transport.

The concept draws inspiration from the ancient Greek Archimedean screw, a device used to lift water through rotation. In the quantum realm, a similar structure—an electron traveling along a spiral nanowire—can induce directed charge flow by cyclically modulating its quantum states.

Unlike conventional currents driven by voltage, this effect involves gradually varying system parameters to achieve a quantized transfer of electrons with each cycle, fundamentally linked to the topological nature of the material.

First proposed by Nobel laureate David Thouless in 1983, topological charge pumping enables electrons to move in discrete steps without applying an external voltage. While this phenomenon has been realized in various engineered systems, the current work demonstrates that a simple modulation of the electric field's direction in a chiral nanowire is sufficient to produce quantized charge transport.

This insight simplifies the pathway toward practical topological devices, eliminating the need for multiple control parameters previously deemed necessary.

Using advanced time-dependent simulations of multiorbital models and density functional theory calculations, the researchers examined electrons in spiral hydrocarbons and selenium nanowires. They found that as electrons are pumped along the wire, orbital angular momentum becomes dynamically polarized. In selenium nanowires, a portion of this orbital polarization converts into spin polarization via spin-orbit coupling, establishing a topological mechanism akin to the chirality-induced spin selectivity (CISS) effect.

Using advanced time-dependent simulations of multiorbital models and density functional theory calculations, the team examined electrons in spiral hydrocarbons and selenium nanowires. They observed that as electrons are pumped along the wire, orbital angular momentum becomes dynamically polarized. In selenium nanowires, part of this orbital polarization converts into spin polarization via spin-orbit coupling, creating a topological mechanism similar to the chirality-induced spin selectivity (CISS) effect.

Professor Park notes, "This work shows that charge, orbital, and spin behaviors are interconnected through a topological process in chiral nanowires. It opens pathways to control these properties electrically at the nanoscale."

Published in the May 2026 issue of  Nano Letters , the study involved Dr. Esmaeil Taghizadeh Sisakht from UNIST. It was supported by the National Research Foundation of Korea (NRF), the Ministry of Science and ICT (MSIT), the Korea Institute for Advancement of Technology (KIAT), and the Ministry of Trade, Industry and Energy (MOTIE).

Journal Reference

Esmaeil Taghizadeh Sisakht, Uiseok Jeong, Xiao Jiang,   et al ., “Spin and Orbital Angular Momentum Polarization in Thouless Topological Charge Pumping,”  Nano Letters,  (2026).