Advances in Topological Pumping Enable Control of Spin Polarization in One-Dimensional Wires

The fundamental physics of charge movement in materials takes a new turn as researchers investigate how spin and orbital angular momentum behave during topological charge pumping, a process where electrical charge is moved in a controlled, quantum manner. Esmaeil Taghizadeh Sisakht, Uiseok Jeong, and Xiao Jiang, all from the Ulsan National Institute of Science and Technology, along with Jinseok Oh, Yizhou Liu, and Binghai Yan, demonstrate that this charge pumping generates spin polarization within insulating materials, offering a fresh perspective on spin-selective transport observed in chiral wires. Their work establishes a simplified mechanism for one-dimensional pumping, relying on the material’s geometry rather than complex parameter adjustments, and reveals a link between charge flow and the emergence of orbital and spin polarization. This discovery suggests a deeper connection between synthetic and real-world topological insulators, potentially paving the way for novel spintronic devices and a better understanding of anomalous charge behaviour in materials.

Detailed Calculations and Model Parameters

This document details the calculations and model parameters used in research on topological materials and Thouless pumping, ensuring reproducibility and credibility. It explains key concepts like Thouless pumping, topological materials, and angular momentum, alongside methods such as tight-binding models and density functional theory. The document breaks down supplementary notes, detailing the construction and validation of a tight-binding model for a chiral hydrocarbon molecule, and the mathematical derivation of how an electric field induces torque on orbital angular momentum during pumping.,.

Chiral Wires Generate Spin Polarization via Pumping

Researchers are exploring how charge movement interacts with spin and orbital properties in one-dimensional chiral wires undergoing topologically quantized charge pumping. Their work demonstrates a new method for generating spin polarization in insulating systems through charge pumping, connecting this to chirality-induced spin selectivity. The team used time-dependent Schrödinger equations to model electron behavior within the chiral structure, employing a unique geometry controlled by a single parameter, simplifying the understanding of one-dimensional pumping. Analysis reveals that each cycle of the driving field produces a quantized amount of pumped charge when the Fermi level resides within a topologically induced gap, and the resulting Berry curvature is an integer Chern number, directly linked to the quantized pump. The study extends the concept of orbital polarization to topological charge pumping, showing how orbital angular momentum accompanies charge flow.,.

Chirality Drives Spin Polarization in Insulators

Scientists have demonstrated a novel mechanism for generating spin polarization within insulators using topologically quantized charge pumping in one-dimensional chiral wires, revealing a pathway to chirality-induced spin selectivity. The research focuses on creating spin currents through charge movement, offering a purely electrical method for spin manipulation. Solving time-dependent Schrödinger equations based on multi-orbital tight-binding Hamiltonians, driven by a circularly polarized electric field, models electron behavior within the chiral wire structure. The unique screw-like geometry of the chiral wire requires only a single control parameter to achieve quantized charge pumping, simplifying conventional methods. Measurements confirm that the pumping process maintains an open energy gap and induces a nonequilibrium orbital polarization, which is partially converted into spin polarization through spin-orbit coupling, with the spin direction determined by the current and chirality. This establishes chiral wires as viable platforms for both orbital and spin-polarized Thouless charge pumping, delivering a new understanding of spin dynamics in chiral materials.,.

Chiral Wires Pump Charge and Angular Momentum

This research demonstrates a novel mechanism for charge pumping in one-dimensional chiral systems, revealing a direct link between topological charge transport and the transfer of angular momentum. Scientists modeled electron behavior within these chiral wires using advanced computational methods, solving the time-dependent Schrodinger equation for a multi-orbital system subjected to an oscillating electric field. The unique screw-like geometry of the system facilitates quantized charge pumping with a simplicity not found in conventional methods, requiring only a single control parameter. The team discovered that this charge flow generates orbital polarization, which is then partially converted into spin polarization via spin-orbit coupling, with the spin direction linked to the electrical current and chirality. This work establishes a pathway where bulk topological properties can be directly measured through observable quantities like orbital or spin angular momentum.