Non-equilibrium polaron hopping transport through DNA

We study the electronic transport through short DNA chains with various sequences of base pairs between voltage-biased leads. The strong coupling of the charge carriers to local vibrations of the base pairs leads to the formation of polarons, and in the relevant temperature range the transport is accomplished by sequential polaron hopping. We calculate the rates for these processes, extending what is known as the $P(E)$-theory of single-electron tunneling to the situation with site-specific local oscillators. The non-equilibrium charge rearrangement along the DNA leads to sequence-dependent current thresholds of the `semi-conducting' current-voltage characteristics and, except for symmetric sequences, to rectifying behavior. The current is thermally activated with activation energy approaching for voltages above the threshold the bulk value (polaron shift or reorganization energy). Our results are consistent with some recent experiments.