Figure 3.

Temperature and oxidation-state dependence of molecular conductance. (a) Fluctuations of conductance and Kondo resonances from interference disappear as thermal energy surpasses hv_F/L (4 meV) and the coherence length decreases, as shown in the conductance map at 80 K (k_BT = 6.9 meV). (b) Experimental differential conductance of the Kondo peak at V_g = −0.85 V (purple circles) and fit to the spin-1/2 Kondo model with T_K = 18 ± 1 K and s = 0.30 ± 0.04 (blue line). Inset: Experimental differential conductance as a function of bias voltage (gray curves) and the Lorentzian fits of Kondo peaks (purple curves). (c) Differential conductance map measured as a function of temperature and gate voltage. Indicative of phase coherent transport, the conductance does not show an obvious temperature dependence. (d) Differential conductance as a function of V_g measured at 5 K (blue curve) and 80 K (pink curve) with a fixed bias voltage V_sd = 10 mV. (e) Temperature dependence of off-resonant transport measured in the conductance minima of the charge states. The values are averaged over a 100 mV window around V_g = −2.90 V for N – 2, V_g = −1.30 V for N – 1, and V_g = 0.6 V for N charge states. We also display the temperature dependence of the N – 2/N – 1 (V_g = −1.75 V) and N – 1/N (V_g = −0.95 V) Coulomb peaks. Note that there is a shift in the position of the Coulomb peaks from Figure 2, probably as a result of a change in trap occupancy in the HfO₂. For (c–e), the conductance was measured at V_sd = 10 mV to exclude the impact of Kondo resonance. (f) Calculated transmission spectra for the neutral state (purple) and oxidized state (orange) of a single-molecule junction. All experimental data in this figure are from Ni-FP8 device 1.