Inelastic electron transport and noise in mesoscopic structures.

摘要

Using the quasiclassical non-equilibrium Green's function method, we have studied the effects of inelastic interactions on the current and noise characteristics of a number of different mesoscopic structures.; First, we considered the influence of electromagnetic fluctuations on the resonant tunneling of electrons through a quantum dot. We show that the overall effect of the fluctuations depends on whether the electron bands in external electrodes are empty or filled. In the empty band case, depending on the relation between the tunneling rate and characteristic frequency of the fluctuations, the field either simply shifts the conductance peak, or broadens it. This is a single-particle regime of electron transport, and can be described by the generalized Landauer formula. For filled bands the problem is essentially multi-electron in character. An important difference with the single-particle regime is that the fluctuations of the resonant level do not suppress the conductance of the filled bands at resonance if the coupling between electrons and electromagnetic modes is weaker than some critical value. At large coupling constants, the conductance at resonance is abruptly suppressed.; Next, we studied the influence of the electromagnetic environment on the noise characteristics of a quantum point contact (QPC) between two normal hulk electrodes. We show that at zero temperature, the zero-frequency spectral density of current fluctuations has a {dollar}Ssb{lcub}I{rcub}=2emiddelta Imid{dollar} dependence, where {dollar}delta I{dollar} is the backflow current due to the interaction between the transport electrons and the environment.; Finally, we investigated the spectral density of current noise in short ballistic superconducting quantum point contacts. We predicted that at small bias voltages, there is a large current noise associated with the supercurrent flow in both regimes of dc and ac Josephson effects. At finite voltages, the noise can be qualitatively understood as the shot noise of the large charge quanta of magnitude {dollar}2Delta/V{dollar} equal to the charge transferred during one period of Josephson oscillations. The effects of junction asymmetry on the dc noise characteristics of the SQPC was also considered.