Elastic tunneling identification through crossings, anti-crossings and splitting of states in the complex electronic current of systems based on mesoscopic molecules

Abstract

We have systematically studied the conductance σ(E,B) and the electronic current line shapes J(Vex) through complex mesoscopic molecules in an elastic resonant tunneling regime. The studied systems are based on GaAs/AlGaAs hetero-structures, with several discrete states in each coupled mesoscopic molecule. The molecules were formed using different wells and barrier widths. These systems allow effective couplings and uncouplings that lead to elastic processes as a function of the electronic potential Vex and magnetic field B. In this situation, the J(Vex) and σ(E, B) curves exhibit a sequence of peaks of difficult interpretation, in which crossings and anti-crossings (a splitting if it is generated in the resonance condition) of states contribute in a way that they cannot be easily identified. Performing a systematic analysis of the evolution of these states (before the resonance condition), we were able to determine the origin of these current peaks. We have found that the coupling of states (anti-crossing) around the resonance region can be identified as a broad mirrored-D line shape in the J(Vex) curves. The mirrored-D line shape peaks can be clearly differentiated from the neighboring peaks because the last ones follow a very defined increasing sequence in their intensities and widths. Also, this behavior (fingerprint) can be used to identify possible splitting of states in the J(Vex). The splittings that are generated between states with different quantum numbers (quantum numbers associated to the individual well) follow an unexpected opposite behavior when compared with those generated between states with the same quantum numbers (quasi-miniband). All these results are also observed in the conductance σ(E, B) associated with complex mesoscopic molecules based on a two-dimensional electron gas.