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

Bijay Kumar Agarwalla,Upendra Harbola,Shaul Mukamel,Yu Zhang,Weijie Hua

doi:10.1063/1.4919955

Bijay Kumar Agarwalla, Upendra Harbola + Show 3 more

Open Access

https://doi.org/10.1063/1.4919955

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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.

Highlights

Ultrafast picosecond to femtosecond processes determine the elementary photophysical and photochemical properties of molecules, for example, the (200 fs) isomerization of rhodopsins1,2 which is the primary step in visual signalling, vibrational relaxation, charge transfer in molecules, and coherent energy transfer in chromophore complexes
We have employed a Liouville space diagrammatic approach to calculate nonlinear coherent stimulated signal and incoherent charge current response from a molecular junction driven by impulsive optical pulses
The signals are calculated to fourth order in the molecule-field interaction

Summary

INTRODUCTION

Ultrafast picosecond to femtosecond processes determine the elementary photophysical and photochemical properties of molecules, for example, the (200 fs) isomerization of rhodopsins which is the primary step in visual signalling, vibrational relaxation, charge transfer in molecules, and coherent energy transfer in chromophore complexes. It is of interest to understand the ultrafast dynamics at the single molecule level since ensemble averaging often obscures the microscopic dynamics. Due to small size of the molecule (comparable to the wavelength of the electromagnetic field), the wavevector matching condition cannot be used to separate different contributions to coherent signals. This can be done by phase cycling protocols.. We use a diagrammatic Liouville space approach to calculate time-resolved signals from a molecular junction Both photon and electronic (current) detections are compared. The photon and electron signals are expressed in terms of molecular correlation functions and expanded in molecular eigenstates, obtained from standard quantum chemistry calculations We apply this formulation to compute signals from a junction made of Benzene-1,4-dithiol molecule.

COHERENT HETERODYNE DETECTED SIGNALS IN MOLECULAR JUNCTION

INCOHERENT ELECTRONIC CURRENT DETECTION OF MULTIDIMENSIONAL SIGNALS

CONCLUSIONS