Chirality-Induced Spin Filtering in Pseudo Jahn-Teller Molecules

TL;DR

This paper presents a theoretical model demonstrating that chiral molecules with pseudo Jahn-Teller effects can act as efficient spin filters, with their effectiveness largely independent of spin-orbit coupling strength, aided by nuclear vibrations.

Contribution

It introduces a novel theoretical framework showing how pseudo Jahn-Teller molecules can induce spin filtering independent of SOC strength, emphasizing the role of nuclear vibrations.

Findings

Spin filtering efficiency can be nearly independent of SOC strength.

Nuclear vibrations enhance the spin-filtering effect.

Chiral molecules can act as effective spin filters through vibrational coupling.

Abstract

Chirality-induced spin selectivity (CISS) refers to an ability to induce a spin polarization of an electron transmitted through chiral materials. An important experimental observation is that incredibly large spin polarization is realized at room temperature even for organic molecules that have weak spin-orbit coupling (SOC), although SOC is the only interaction that can manipulate the electrons' spins in the setups. Therefore, the mechanism of the CISS needs to be constructed in a way insensitive to or enhancing the magnitude of the SOC strength. In this paper, we describe a theoretical study of CISS with a model chiral molecule that belongs to the point group $\mathrm{C}_3$. In this molecule, electronic translational and rotational degrees of freedom for an injected electron are coupled to one another via the nuclear vibrational mode with a pseudo Jahn-Teller effect. By properly taking the molecular symmetry as well as the time-reversal symmetry into account and classifying the molecular ground states by their angular- and spin-momentum quantum numbers, we show that the chiral molecule can act as an efficient spin filter. The efficiency of this spin filtering can be nearly independent of the SOC strength in this model, while it well exceeds the spin polarization relying solely on the SOC. The nuclear vibrations turned out to have the role of not only mediating the translation-rotation coupling, but also enhancing the spin-filtering efficiency.