Double versus single junction: From tunneling to contact regime in a double quantum dot molecule system

Abstract

In this work a theoretical study of the charge transport through a nanostructure composed by a double quantum dot was made by treating the system in two different ways: as single junction (SJ) within the scanning tunneling microscopy theory and a double junction (DJ) within the usual non equilibrium Green's function theory approach. In the first case (SJ), the three blocks – contact-device-contact – is treated as a single junction by ‘breaking’ the nanostructure into two parts and considering each one as belonging to an ‘extended contact’. In the DJ case, the usual treatment with two contacts-related broadening and the exact Green's function describing the propagation inside the system was made. Proceeding in this way, for a minimum two-level model system, we show that the results obtained with the SJ and DJ treatment are identical despite they start with a different general formulae for transmission. Finally, both treatments were used with a minimal model for a biphenyl system in an asymmetric sample-biphenyl-tip configuration and analyzed in terms of a SJ point of view bringing another perspective to the main features of this system.