Differential tunnel resistance

Fig. 10.10 The differential tunnel resistance dV/d/of (BEDT-TTF)2l3 in the superconducting state at various temperatures T. 4Aj is the full width at d V/dl = 0 and is a measure of the band gap at the given temperature T (see text).

Fig. 5.24. Differential conductance dl/dV as a function of bias voltage of an AI-AI2O3 - amorphous Ge tunneling diode (after Osmun and Fritzsche (1970)). At low temperatures the resistance of the a-Ge electrode becomes comparable with the tunnel resistance. The bias voltage across the oxide barrier is then smaller than the applied bias shown here.

Figure 11. Experimental and predicted differential conductance plots of the double-island device of Figure 10(b). (a) Differential conductance measured at 4.2 K four peaks are found per gate period. Above the threshold for the Coulomb blockade, the current can be described as linear with small oscillations superposed, which give the peaks in dljdVj s- The linear component corresponds to a resistance of 20 GQ. (b) Electrical modeling of the device. The silicon substrate acts as a common gate electrode for both islands, (c) Monte Carlo simulation of a stability plot for the double-island device at 4.2 K with capacitance values obtained from finite-element modeling Cq = 0.84aF (island-gate capacitance). Cm = 3.7aF (inter-island capacitance). Cl = 4.9 aF (lead-island capacitance) the left, middle and right tunnel junction resistances were, respectively, set to 0.1, 10 and 10 GQ to reproduce the experimental data. (Reprinted with permission from Ref [28], 2006, American Institute of Physics.)...

Our simple calculation thus reflects the well-known result [1-6] that the differential resistance measured in the tunneling current through an STM tip is proportional to the local DOS of the molecule at the tip. In this section, we did not use any concrete model for the Hamiltonian, the only assumption we needed to make was that the molecule is much more strongly coupled to the metal surface than to the tip, which, at least for metallic surfaces, is always the case. 

In this paper, we report measurements of the low temperature differential resistance of mesoscopic FS junctions. We observe asymmetries in the differential resistance even in the absence of an external magnetic field. These asymmetries are associated with spin-polarized tunneling into the superconductor, with the splitting of the quasi-particle density of states in the superconductor arising from the magnetic field generated by the ferromagnetic elements. 

The Coulomb blockade effect was originally observed in experiments on small metallic or superconducting particles [138-141], in which nanometer-sized metallic grains were embedded within a metal oxide-metal tunnel junction. Electronic measurements performed on these systems at low temperatures (T 1 K) revealed an anomalous behavior of the resistance (or differential capacitance) at zero bias. It was realized that this behavior was caused by the extremely small capacitance of the metallic particles. In a simple model, a spherical particle of diameter d embedded in a... 

Negative differential resistance can also be observed for surfaces with localized trap states. A tunnelling electron can become localized for long times in these surface states, when they are in resonance with the Fermi level of the tip. Electrons so localized electrostatically repel other electrons causing a decrease in tunnelling current, referred to as a coulomb blockade. The voltage at which the NDR occurs is a measure of the energy of the localized trap state. 

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