Knot-Driven Spin Selectivity: Topological Chirality-Induced Robust Spin Polarization in Molecular Knots

TL;DR

This paper introduces a theoretical framework explaining how topological chirality in molecular knots leads to high spin polarization and conductivity, revealing a new mechanism for spin selectivity in nonmagnetic materials.

Contribution

It establishes the first fundamental theory for topological chirality-induced spin selectivity in trefoil knot molecules and identifies conditions for robust spin polarization.

Findings

Trefoil knot molecules can achieve over 60% spin polarization.

Spin polarization remains robust under strain and lattice variations.

Transitioning from topological to trivial structures reduces spin polarization sharply.

Abstract

Compared to traditional structural chiral materials (e.g., DNA, helicene), topological chirality in trefoil knot molecules has demonstrated multiple remarkable advantages in chirality-induced spin selectivity (CISS), including ultra-high spin polarization of nearly 90%, conductivity increased by two orders of magnitude, and high-temperature stability (up to 350$^{\circ}$C). However, the underlying physical mechanism remains elusive. This work establishes, for the first time, a fundamental theoretical framework for topological chirality-induced spin selectivity (TCISS) in trefoil knot molecules and identifies the necessary conditions for knot-driven spin selectivity. Our calculation results reveal that a trefoil knot molecule can exhibit spin polarization exceeding 60% along with significant conductivity. Notably, neither reducing the lattice number nor applying strain regulation significantly diminishes this ultra-high spin polarization, highlighting its robustness. Importantly, when the topological knot degenerates into a trivial structure, accompanied by the transition from topological chirality to structural chirality, the spin polarization sharply declines, demonstrating a strong correlation between the ultrahigh spin polarization and the knot topology. Our theory not only successfully elucidates the physical mechanism of TCISS, but also uncovers a new spin-polarized transport phenomenon termed knot-driven spin selectivity, offering new guiding principles for designing nonmagnetic materials for spintronics device applications.