Nonlinear conductance fluctuations in quantum wires: Appearance of two different energy scales

Using a nonequilibrium Green-function formalism we study numerically the conductance fluctuations in a quantum wire as a function of the applied bias. This system is represented by a tight-binding Hamiltonian with random site energies and the current through the wire is expressed in terms of a transmission coefficient that can be computed by a recursive algorithm. We analyze the fluctuations in the transmission and in the differential conductance for different degrees of disorder, in the limit where the applied bias is much larger than the Thouless correlation energy ${\mathit{E}}_{\mathit{c}}$. In addition to the expected fluctuations in the ${\mathit{E}}_{\mathit{c}}$ scale the conductance has also large random oscillations in a second energy scale related to the motion in the transverse direction. Electron heating effects are included in the model by means of an approximate self-energy, taking into account electron-electron interactions. An estimate is given of the typical voltage scales at which the effects described in this work might be observed in real metallic and semiconducting wires.