# Spin-current induced mechanical torque in a chiral molecular junction

## TL;DR

This paper demonstrates that spin-polarized currents can induce a mechanical torque in chiral molecules like DNA due to spin-orbit interactions, linking spin transport to mechanical effects.

## Contribution

It introduces a microscopic model connecting spin current non-conservation with mechanical torque in chiral molecules, highlighting a novel spin-mechanical coupling mechanism.

## Key findings

- Spin-polarized current generates torque on DNA.
- Spin-orbit interaction causes spin-current non-conservation.
- Mechanical rotation of DNA can be induced by spin injection.

## Abstract

We analyse the appearance of a mechanical torque that acts on a chiral molecule: a single-stranded DNA, in which the spin-orbit interaction is expected to induce a spin-selectivity effect. The mechanical torque is shown to appear as a result of the non-conservation of the spin current in the presence of the spin-orbit interaction. Adopting a simple microscopic model Hamiltonian for a chiral molecule connected to source and drain leads, and accounting for the mechanical torque acting on the chiral molecule as the back action on the electrons traversing the molecule, we derive the spin continuity-equation. It connects the spin current expressed by a Landauer-type formula and the mechanical torque. Thus, by injecting a spin-polarized current from the source electrode, it is possible to generate a torque, which will rotate the DNA molecule.