Understanding resonant charge transport through weakly coupled single-molecule junctions

Abstract

Off-resonant charge transport through molecular junctions has been extensively studied since the advent of single-molecule electronics and is now well understood within the framework of the non-interacting Landauer approach. Conversely, gaining a qualitative and quantitative understanding of the resonant transport regime has proven more elusive. Here, we study resonant charge transport through graphene-based zinc-porphyrin junctions. We experimentally demonstrate an inadequacy of non-interacting Landauer theory as well as the conventional single-mode Franck–Condon model. Instead, we model overall charge transport as a sequence of non-adiabatic electron transfers, with rates depending on both outer and inner-sphere vibrational interactions. We show that the transport properties of our molecular junctions are determined by a combination of electron–electron and electron-vibrational coupling, and are sensitive to interactions with the wider local environment. Furthermore, we assess the importance of nuclear tunnelling and examine the suitability of semi-classical Marcus theory as a description of charge transport in molecular devices.

Functional Redox‐Active Molecular Tunnel Junctions

“…In redox-active molecular junctions, electron-vibration interactions cannot be neglected. For instance, Thomas et al [45] observed vibrational excitations in junctions (Figure 7c) based on zinc-porphyrin compound 12. As shown in the charge stability diagram (Figure 7d), the equally spaced conductance lines (indicated with arrows) are assigned to vibrational modes of the molecule.…”

“…As shown in the charge stability diagram (Figure 7d), the equally spaced conductance lines (indicated with arrows) are assigned to vibrational modes of the molecule. To model charge transport in this molecular junction, Thomas et al [45] employed the model by Sowa et al [16d] (Section 2.5), and the excellent agreement between experiment and theory allowed them to identify the vibrational models involved with charge transport. Vibrational excitations have been frequently observed in other studies as well.…”

“…In redox‐active molecular junctions, electron‐vibration interactions cannot be neglected. For instance, Thomas et al [45] . observed vibrational excitations in junctions (Figure 7c) based on zinc‐porphyrin compound 12 .…”

“…As shown in the charge stability diagram (Figure 7d), the equally spaced conductance lines (indicated with arrows) are assigned to vibrational modes of the molecule. To model charge transport in this molecular junction, Thomas et al [45] . employed the model by Sowa et al [16d] .…”

Generalized input-output method to quantum transport junctions. II. Applications

“…Advanced ex-perimental techniques [3][4][5][6][7][8][9][10][11][12][13][14][15] have led to the discovery of a variety of intriguing many-body phenomena in molecular junctions (MJs) in a metal-moleculemetal motif [16][17][18][19] , including length and temperaturedependent charge transfer 12,13,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] , quantum interference effects 14,[36][37][38][39][40] , molecular thermoelectricity [41][42][43][44] , giant magnetoresistance 45 , Kondo resonance 46,47 , chirality induced spin selectivity [48]…”