Figure 4:

(a) Energy dependence of decay length: Dependence of the inverse decay length ¹/_λ on the square root of the difference between the injection energy and the resonance peak, showing that the decay length depends on the injection energy of the carriers. However the slope and intercept of the fit are not consistent with a simple tunneling process. (b) Injection into allowed states: Conductance as a function of electrode potential for CTPR8 (data for Peak II). Black squares are Pd/Pd relative to a reference electrode, here presented on the NHE scale. Red squares are for other metal combinations (as labeled) with potentials as listed in Tables S2 and S3. The red line is a fit of the Pd/Pd data to the Breit-Wigner formula for resonant tunneling and the blue line is a fit to the formula for a two-step hopping process (Eqn. 3). Both processes may apply: The Breit-Wigner formula describing the first resonant injection from the electrodes and the two-step model describing the individual hops within the bulk of the protein.