Optical Switching of Charge Transmission through a Single Molecule: Effects of Contact Excitations and Molecule Heating

Abstract

Photoinduced changes of the current voltage (IV) characteristics of a single molecule attached to a left and a right electrode are revisited including the inevitable photon absorption by the leads due to electron-hole pair generation. To determine the related nonequilibrium electron distribution, a method is utilized based on the introduction of an effective electron temperature T el in the Fermi distribution. By varying T el , possible excitation conditions in the experiments are modeled. Heating of the molecule as well as the effect of intramolecular vibrational energy redistribution (IVR) is also accounted for. An intermediate excitation regime can be identified where the optical current switch is dominated by molecular excitations and less by an electron-hole pair generation in the leads. Vibrational distributions in the molecule induced due to either current formation or optical excitation are found to strongly deviate from thermal equilibrium. To observe the current switch, it is essential that these distributions are only slightly affected by IVR.

Charge transmission through single molecules: Effects of nonequilibrium molecular vibrations and photoinduced transitions

“…If it is decreased compared to the values used so far the change of the current due to photoexcitation is strongly reduced [61]. This is related to the fact that the degree to achieve a nonequilibrium vibrational distribution is affected by nuclear rearrangement related to charging or discharge.…”

“…[11,13]) connected with the typical restriction to a linear electron-vibrational coupling. To avoid this we utilize a description of the molecule (attached to the leads) in terms of respective electron-vibrational states (this has been already suggested in [18] and used in numerous own computations [26,[58][59][60][61] as well as in [49,27]). Such a representation would offer the most direct way to account for nonequilibrium distributions of intra-molecular vibrations, lately for those which couple most strongly to the charging and discharge processes.…”

“…The absence of any molecular excitation, however, can be achieved if the external field is off-resonant with respect to the electronic transition in the molecule [61]. The middle panel of Fig.…”

“…This approach is particularly suited for the description of transient currents, but will be reduced here to rate equations, thus indicating in a steady state situation the compatibility of the density matrix approach with earlier computations of [26,[58][59][60][61]. The studies are carried out for a standard configuration of a single molecule attached to a left (L) and a right (R) lead (see Fig.…”

Molecular nanoplasmonics: Self-consistent electrodynamics in current-carrying junctions

“…47 Usually in such studies the electromagnetic (EM) field is assumed to be an external driving force. [51][52][53][54][55][56][57][58][59][60][61][62] Recently we utilized the nonequilibrium Green function technique to study the transport and optical response of a molecular junction subjected to external EM field taking into account near-fields driven by SPP local modes, specific for a particular junction geometry.…”