Asymmetric I-V curves

Asymmetric conductors have isymmetric I — V curves. This phenomenon is known as the diode or ratchet effect and plays a major role in electronics. Recently much interest has been attracted by transport asymmetries in singlemolecule devices and other mesoscopic systems [1], The idea that asymmetric molecules can be used as rectifiers is rather old [2], however, it was implemented experimentally [3] only recently. Another experimental realization of a mesoscopic rectifier is an asymmetric electron waveguide constructed within the inversion layer of a semiconductor heterostructure [4]. The ratchet effect was observed in carbon nanotubes [5], and strongly asymmetric I — V curves were recently reported for the tunneling in the quantum Hall edge states [6]. These experimental advances have stimulated much theoretical activity [7, 8, 9, 10, 11] with the main focus on the simplest Fermi-liquid systems [12]. 

The voltage dependence predicted by (2) leads to a highly nonlinear I(V) curve if plotted over a bias of several volts. If the barrier is sufficiently asymmetrical at zero bias, the I(V) curve becomes asymmetrical as well as nonlinear. Such a curve is shown in the lower part of Fig. 2. Equations for more complicated zero-bias barriers, such as the combination of a trapezoid and a square barrier, have been given by several authors [40, 41], Equations like (2) and those for more complex barriers can provide information about barrier height and barrier thickness [30, 40-45]. 

Further, we studied the nonequilibrium current for large bias-voltages (Fig. 26). Because e iCoulomb interaction, the I-V curve is asymmetric for Vbias> and there are one step and one maximum for the current. The step contributes to one peak for the conductance. When we introduce the Coulomb interaction to the... 

Scanning tunneling spectroscopic studies of Y-junction carbon nanotubes show interesting diodelike device characteristics at the junctions. A typical /—V curve obtained from positioning the tip atop a Y-Junction (the point of contact between the three arms) as well as on the individual arms of the Y-junction is shown in Figure 10. The I—V plot at the junction is asymmetric (Figure 10b)... 

The as3nnmetry of I-V and G-V curves (fig. la) has to be related to an asymmetrical distribution of the protein between the two sides of the membrane, that is MCh interacts with the bilayer opening a channel but cannot pass throughout it. In this way all the molecules maintain the same orientation one face immersed into the hydrophobic region, where they suffer almost the whole potential drop, and one face in the hemocyanin containing water solution. 

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