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Dynamical coupling and negative differential resistance from interactions across the molecule-electrode interface in molecular junctions
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View: Figures


Image of FIG. 1.
FIG. 1.

Schematic representation of the molecular junction under consideration. When an electron hops from the bridging site to the LUMO, a hole is left behind. Due to the interface Coulomb interaction, the electron on the LUMO and the hole on the bridging site are attracted, forming a bound exciton. This process renormalizes and enhances the tunneling matrix element between the bridging site and the LUMO, thereby affecting the current through the junction.

Image of FIG. 2.
FIG. 2.

I-V curves for the molecular junction for different values of the interface Coulomb interaction, = 0, 0.4, …, 2.8 eV (see text for other numerical parameters). As increases, the current develops a peak near the LUMO resonance and NDR. (Inset) Blow-up of current at low bias, demonstrating an increase in the conductance with increasing .

Image of FIG. 3.
FIG. 3.

Current (blue) and effective coupling Γ (red) as a function of the bias voltage for the interface Coulomb interaction = 2.6 eV. The coupling constant is maximal at the LUMO resonance, followed by a peek in the current. In the inset the experimental data of Ref. 5 is shown, presenting the current (blue) and force constant (red). The dashed lines show the position of the maximum coupling, demonstrating the agreement between theory and experiment.

Image of FIG. 4.
FIG. 4.

(a) The parts (ω) + (ω) (blue line) and ℜ ω (purple line) composing the integrand (ω) (Eq. (6) ), for a non-interacting example (see text). ℜ ω changes sign as the molecular level is crossed. (b) (ω) for different bias voltages = 0, 0.1, 0.2, 0.3. As long as < ε, (ω) is mostly positive, and reaches maximal area when = ε (dashed line), after which it develops a negative part, resulting in a decrease in τ.

Image of FIG. 5.
FIG. 5.

Peak-to-valley ratio (PVR) as a function of the molecule-electrode distance , which affects both the interface interaction and the bare tunneling elements (see text). The strong dependence of the PVR on can be tested experimentally, and is in accord with the experimental findings. (Inset) I-V curves for different temperatures = 60, 120, …, 300 K, demonstrating a very weak dependence of the current on the temperature. This weak dependence can also serve as a test for the origin of the NDR.

Image of FIG. 6.
FIG. 6.

Power output vs. bias voltage of the molecular junction in the presence of a constant temperature gradient Δ = 50 K, for = 2.6 eV (blue solid line) and = 0 eV (dashed red line).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Dynamical coupling and negative differential resistance from interactions across the molecule-electrode interface in molecular junctions