Comment on: "Spin-orbit interaction and spin selectivity for tunneling electron transfer in DNA"

TL;DR

This paper critically examines a recent model claiming to explain spin selectivity in DNA tunneling and demonstrates that the model cannot produce the claimed spin asymmetry, challenging its validity in explaining CISS.

Contribution

The authors analytically solve the proposed model and show it does not generate spin asymmetry, refuting its ability to explain chiral-induced spin selectivity in biological molecules.

Findings

The model does not produce spin asymmetry in tunneling.

Time-reversal symmetric Hamiltonian cannot generate spin selectivity.

The proposed explanation for CISS in DNA is invalid.

Abstract

The observation of chiral-induced spin selectivity (CISS) in biological molecules still awaits a full theoretical explanation. In a recent Rapid Communication, Varela et al. [Phys. Rev. B 101, 241410(R) (2020)] presented a model for electron transport in biological molecules by tunneling in the presence of spin-orbit interactions. They then claimed that their model produces a strong spin asymmetry due to the intrinsic atomic spin-orbit strength. As their Hamiltonian is time-reversal symmetric, this result contradicts a theorem by Bardarson [J. Phys. A: Math. Theor. 41, 405203 (2008)], which states that such a Hamiltonian cannot generate a spin asymmetry for tunneling between two terminals (in which there are only a spin-up and a spin-down channels). Here we solve the model proposed by Varela et al. and show that it does not yield any spin asymmetry, and therefore cannot explain the observed CISS effect.