Contact-dependent effects and tunneling currents in DNA molecules

We report on theoretical results about contact-dependent effects and tunneling currents through DNA molecules. A tetranucleotide PolyGACT chain, connected in between metallic contacts, is studied as a generic case, and compared to other periodic sequences such as PolyAT or PolyGC. Remarkable resonance conditions are analytically derived, indicating that a strong coupling does not always result in a larger conductance. This result is properly illustrated by considering intrinsic features of bias-dependent tunneling currents in the coherent regime.

Figure 1

Transmission coefficient curve for a polyGACT chain with $N=60$, $t_m=1.0\mathrm{eV}$, $t=0.4\mathrm{eV}$, and $\tau =0.4\mathrm{eV}$ (top panel); $\tau =\sqrt{0.4}\mathrm{eV}$ (central panel); and $\tau =0.8\mathrm{eV}$ (bottom panel).

Figure 2

Main frame: Tunneling currents for several $N=10$ sequences (PolyG, PolyAT, and polyGC) with parameters $t_m=1.0\mathrm{eV}$, $t=1\mathrm{eV}$, $\tau =1\mathrm{eV}$, and ${\epsilon }_m=5.36\mathrm{eV}$. Inset: Tunneling current through a $N=60$ PolyG sequence with $t_m=1.0\mathrm{eV}$, $t=1\mathrm{eV}$, $\tau =1\mathrm{eV}$, ${\epsilon }_m={\epsilon }_G$.

Figure 3

Main frame: Tunneling currents for several periodic PolyGACT-based sequences with parameters $t_m=12.0\mathrm{eV}$, $t=1\mathrm{eV}$, $\tau =1\mathrm{eV}$, and ${\epsilon }_m=5.36\mathrm{eV}$. Inset: Tunneling currents for PolyGACT sequences with $N=8$ (GACTGACT), $N=10$, and $N=12$, with parameters $t=0.4\mathrm{eV}$, and $\tau =\sqrt{0.4}\mathrm{eV}$ (bottom inset) or $\tau =\sqrt{4.8}\mathrm{eV}$ (top inset).