Transient switch-on/off currents in molecular junctions

Abstract

Based on the nonequilibrium density matrix theory we put forward a unified description of the transient and the steady state current formation through a molecular junction. It is demonstrated that the current follows the time evolution of the populations of those molecular charged states which participate in the inter-electrode charge transmission. As an example, the formation of switch-on/switch-off currents is analyzed for a junction where the molecule has two active terminal sites. It is shown that just after a sudden voltage switch-on or switch-off, the resulting transient currents can significantly exceed their steady state value. This feature is caused by molecular charging or discharging processes, which are fast compared to those processes responsible for establishing the steady state current in the junction. The largest transient currents appear if the coupling of the molecule to the adjacent electrodes is asymmetric, or if the applied voltage causes a transformation of extended molecular states into localized ones.

Conductance Mechanism in a Linear Non-Conjugated Trimethylsilyl-Acetylene Molecule: Tunneling Through Localized States

“…Therefore, it is more convenient to employ a description based on the kinetic theory of charge transmission. Last years this theory has been adapted especially for the studies of transient and steady state currents in molecular junctions [39][40][41][42][43][44].…”

“…In line with the kinetic theory, a tunnel current I through the LMR-system can be calculated with use of expression [39,41,42,44] …”

Kinetics of current formation in a molecular diode

“…In this case, the molecular states participate in the process in a virtual manner, i.e., the transported electron is not trapped on the molecule contrary to the case of sequential transport. Thus, for the direct inter-electrode transport it holds that I Below we apply the kinetic theory of electron transport through a molecule (see Refs.14,18,and 19) in such 1M2-systems where the Coulomb charge repulsion of excessive electrons/holes on the molecule is so large that at a given potential difference V the molecule can be either in a neutral ground state ( ¼ 2), neutral excited state ( ¼ 2 * ) or singly charged states ( ¼ 1 and ¼ 3). In the presence of this Coulomb blockade type, the total current through electrode r is…”

Transient currents in a molecular photo-diode

“…Respective transfer rates are presented in refs. [38,42]. The mechanism of electron-pair transitions has been applied earlier to explain the nonlinear electron transport through a single-level quantum dot [44].…”

“…3.] An additional interpretation of the transmission gaps follows from a comparison of electron energies belonging the whole 1-M-2 system [38,39]. Let E e be the energy of electrons in the electrodes.…”