Nonlinear Differential Conductance Research Articles

Anisotropy of zero-bias diffusive anomalies for different orientations of an external magnetic field

We consider the influence of the electron-electron interaction on the nonlinearity of the current-voltage characteristic of the tunnel junction at low bias (diffusive anomaly) in the presence of the classical magnetic field. We present the theory of a phenomenon which manifests itself in the strong anisotropy of a diffusive anomaly for different orientations of the magnetic field with respect to the interface of the tunnel junction. The nonlinear differential tunneling conductance has a universal magnetic field dependence, so that only the magnetic field component perpendicular to the interface is involved. In particular, when the magnetic field is parallel to the interface, the $I$-$V$ characteristic does not depend on the value of the magnetic field.

Anderson model out of equilibrium: Noncrossing-approximation approach to transport through a quantum dot.

The infinite-U Anderson model is applied to transport through a quantum dot. The current and density of states are obtained via the noncrossing approximation for two spin-degenerate levels weakly coupled to two leads. At low temperatures, the Kondo peak in the equilibrium density of states strongly enhances the linear-response conductance. Application of a finite voltage bias reduces the conductance and splits the peak in the density of states. The split peaks, one at each chemical potential, are suppressed in amplitude by a finite dissipative lifetime. We estimate this lifetime perturbatively as the time to transfer an electron from the higher-chemical-potential lead to the lower-chemical-potential one. At zero magnetic field, the clearest signatures of the Kondo effect in transport through a quantum dot are the broadening, shift, and enhancement of the linear-response conductance peaks at low temperatures, and a peak in the nonlinear differential conductance around zero bias.

Quantisation of the conductance in units of e 2/2h in a ballistic quasi-one-dimensional channel, produced by strong electric and magnetic fields

We present data for the differential conductance of a quantum point contact under both strong electric and magnetic fields that shows quantisation in units of e 2/2h, proving that the spin-splitting and the bias-induced-splitting of the plateaux are two independent effects. Calculations of the non-linear differential conductance, using a saddle-point potential to model (1) the one-dimensional channel and assuming that half of the applied source-drain voltage is dropped between each of the contacts and the centre of the channel (2), show excellent agreement with the experimental data.

Experimental study of the frequency limits of a resonant tunneling oscillator

An equivalent circuit obtained from microwave impedance and power data is proposed for a resonant tunneling diode. The four-element circuit consists of a series R and C in parallel with a nonlinear negative differential conductance −G, the combination in turn in series with a resistor r. The resistive cut-off frequency predicted by this model depends on both the RC and RG products. Detection at THz frequencies is also explained by the model.

Travelling Waves on a Josephson Transmission Line

Various properties of stationary travelling waves propagating along a Josephson transmission line having positive nonlinear differential tunnelling conductance and distributed bias current are discussed geometrically in the state plane. First, the change of patterns of solutions in the state plane is uniquely determined for changes in conductance, fluxon velocity and bias current. Second, it is demonstrated that for the linear component of the conductance only, an event takes place in which the solitary wave velocity does not reach the velocity of the electromagnetic waves on a dissipationless transmission line in the certain limit of bias current. Finally, it is shown numerically that the non-linearity of the conductance has important effects on the waves, both quantitatively and qualitatively.