Spin-Current Induced Mechanical Torque in a Chiral Molecular Junction

Abstract

We analyse the appearance of a mechanical torque that acts on a chiral molecule: a singlestranded 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. arXiv:1902.01152v1 [cond-mat.mes-hall]

Theory of Chirality Induced Spin Selectivity: Progress and Challenges

“…While such a framework cannot be ruled out, chirality‐induced spin selectivity may perhaps be thought of as a set of phenomena that have a unifying scheme only in the sense that they all derive from the interplay of spin–orbit interaction and chirality. For example, it has been suggested theoretically that spin–orbit interaction leads to non‐conservation of spin currents in a two‐terminal junction and consequently to a mechanical torque, [ 109 ] which is a different experimental observable than the ones surveyed above. Such a CISS‐induced torque has indeed been suggested as an explanation for a recent experiment demonstrating the use of a chiral molecule as a molecular motor.…”

Spin selectivity through time-reversal symmetric helical junctions

“…In our case, ∆h/R = 18.1 (see Ref. 44), and thus the 'normalized' curvature is κ ≈ 0.33. The spin polarization seems to be sensitive to perturbations which mix left-and right-going waves, such as interface scattering and scattering between the sub systems induced by a finite torsion [see Sec.…”

“…7 result from the interplay between the helical structure and the spin-orbit interaction. Such an interplay has been pointed out before for the Rashba-type SOI, where it appeared as a cutoff of the period of oscillation of the mechanical torque (which is equivalent to spin current) as a function of the length of molecule 44 .…”

Theory of Chirality Induced Spin Selectivity: Progress and Challenges

“…While such a framework cannot be ruled out, chirality-induced spin selectivity may perhaps be thought of as a set of phenomena that have a unifying scheme only in the sense that they all derive from the interplay of spinorbit interaction and chirality. For example, it has been suggested theoretically that spin-orbit interaction leads to non-conservation of spin currents in a two-terminal junction and consequently to a mechanical torque [102], which is a different experimental observable than the ones surveyed above. Such a CISS-induced torque has indeed been suggested as an explanation for a recent experiment demonstrating the use of a chiral molecule as a molecular motor [103].…”