Resonant Electron Dynamics in Open Nano Scale Systems: A Time-Dependent Non- Equilibrium Green Function Approach.

Abstract

Research in nanometer length scale electronics is motivated by both a desire to understand the physics of such small systems and the technological advantages of implementing ever smaller more efficient devices. Ongoing experimental research is focused on characterizing the temporal response of nano-electronics to both weak and strong time-dependent classical driving fields. Theoretical models and methods are also being developed and implemented to explain these experiments. In particular, the weak classical driving field scenario offers the opportunity to efficiently model the response of the manifold of states to the driving field. This two variable (state energy and time) problem is the focus of this dissertation. A two-variable non-equilibrium Green function (NEGF) based time-dependent perturbation theory (TDPT) is developed and applied to small model two and four state systems. This formalism is used to study the dynamic interplay between a source drain bias and a resonant laser excitation that induces coherences and transfers population between states and out of the device. A unique effect in which laser induced population inversion between states brings about a reversal of current direction (absolute negative conductance) is reported. Finally, a one variable constant constant potential theory (CPT), is derived and compared to Landauer theory for simple systems.