Description
Controlling charge and spin transport in single-molecule junctions is a central goal of molecular electronics. An external optical field is attractive as a transport control strategy: it is fast, reversible, and carries its own internal degree of freedom from the handedness of polarisation. Circularly polarised light (CPL) is particularly compelling because it breaks time-reversal symmetry without an external magnetic field. This poses potential for all-optical, handedness-selective control of molecular conductance, and of optically induced spin selectivity, with applications in molecular spintronics, photo-switchable devices, and chiral sensing.
We present a Floquet–nonequilibrium Green's function (Floquet-NEGF) theory to realise this prospective control strategy, through aromatic compounds coupled to metallic leads in the nonequilibrium regime, under driving by an off-resonant CPL field. Within a tight-binding description of the π-electron manifold, the light-matter coupling enters through a Peierls substitution that dresses each hopping amplitude with a bond-dependent, time-periodic phase. The Jacobi-Anger expansion of the dressed hopping yields a multiphoton Floquet replica structure where the Bessel weights set the photon-assisted tunnelling amplitudes, and the chirality-sensitive phases control interference between transport channels. We then extract the time-dependent current, time-averaged differential conductance, and the photon-resolved transmission, and identify regimes of coherent destruction of tunnelling (CDT) near the zeros of dressed hopping amplitudes.
Three families of systems are analysed: benzene, as a closed-shell benchmark; heteroatomic rings, to produce tuneable chiral response; and fused polycyclic rings, where multiple interpenetrating current loops support a richer interference landscape and size-dependent Floquet resonances. Each resulting photoconductance and current dichroism are quantified.
These results show that the handedness of an optical drive, combined with the geometry and heteroatom content of the conjugated ring, provides a set of independent controls over quantum transport. The framework establishes a systematic route to light-driven chiral electronics and optically induced spin selectivity in molecular conductors.
| I am the presenting author | Yes |
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