Coherent (photon) vs incoherent (current) detection of multidimensional optical signals from single molecules in open junctions

Abstract

The nonlinear optical response of a current-carrying single molecule coupled to two metal leads and driven by a sequence of impulsive optical pulses with controllable phases and time delays is calculated. Coherent (stimulated, heterodyne) detection of photons and incoherent detection of the optically induced current are compared. Using a diagrammatic Liouville space superoperator formalism, the signals are recast in terms of molecular correlation functions which are then expanded in the many-body molecular states. Two dimensional signals in benzene-1,4-dithiol molecule show cross peaks involving charged states. The correlation between optical and charge current signal is also observed. C 2015 AIP Publishing LLC. [http://dx

Simulation of optical response functions in molecular junctions

“…[54] we now specify to 4-laser pulse sequence for time domain experiment. Radiation field (14) takes the form…”

“…Quantum regression theorem [55] is the usual choice in nonlinear optical spectroscopy [17]. For example, recent works on optical spectroscopy in junctions [53,54] utilize this approach. Within the approach interactions with the field define time intervals in which evolution of the system is governed by reduced Liouvillian.…”

“…In Section III we specialize our formulation to description of coherent multi-dimensional optical signals in junctions following recent consideration in Ref. [54]. Section IV concludes.…”

“…Recently, we utilized the approach to generalize our previous quasiparticle (orbital) based formulations for Raman spectroscopy in molecular junctions [42][43][44][45] to account exactly for dependence of molecular normal modes on charging state of the molecule [57]. Here we utilize the nonequilibrium atomic limit tools to complement traditional nonlinear optical spectroscopy formulations [53,54].…”

“…In molecular junctions the formulation is complemented by quantum master equation (QME) to account for current carrying state of the system [53,54]. Molecular spectroscopy is characterized via response functions obtained from perturbative expansion of photon flux in molecular interaction with radiation field, which requires evaluation of multi-time correlation functions.…”