Large-bandgap behavior in transport of electrons through individual DNA molecules caused by coupling with a two-level system

We propose a model to interpret the large-bandgap behavior in transport of electrons through an individual DNA molecule where the tunneling electrons are coupled with two-level systems (TLS). The TLS can be regarded as the simplest way to describe vibrations and inelastic scattering in the molecules if the two levels represent the low-lying phonon states. The nonlinear current-voltage curves can be derived by the use of the transfer matrices in an equivalent single-particle multichannel network. At low temperatures, the gap of the conduction band is sensitive to the strength of the coupling between the TLS and the conduction electrons. It is shown that the large-bandgap behavior similar to that of semiconductors stems from the inelastic scattering by the TLS.