scholarly journals Optical spectroscopy of molecular junctions: Nonequilibrium Green’s functions perspective

2016 ◽  
Vol 144 (17) ◽  
pp. 174113 ◽  
Author(s):  
Yi Gao ◽  
Michael Galperin
Keyword(s):  
Optical Spectroscopy ◽  
Green's Functions ◽  
Green’S Functions ◽  
Molecular Junctions ◽  
Nonequilibrium Green’S Functions ◽  
Nonequilibrium Green's Functions

Nonequilibrium Green’s Functions

2018 ◽  
Author(s):  
Klaus Morawetz
Keyword(s):  
Green’S Function ◽  
Quantum Transport ◽  
Green's Function ◽  
Green's Functions ◽  
Green’S Functions ◽  
Equation Of Motion ◽  
Diagrammatic Technique ◽  
Initial Correlations ◽  
Nonequilibrium Green’S Functions ◽  
Nonequilibrium Green's Functions

The method of the equation of motion is used to derive the Martin–Schwinger hierarchy for the nonequilibrium Green’s functions. The formal closure of the hierarchy is reached by using the selfenergy which provides a recipe for how to construct selfenergies from approximations of the two-particle Green’s function. The Langreth–Wilkins rules for a diagrammatic technique are shown to be equivalent to the weakening of initial correlations. The quantum transport equations are derived in the general form of Kadanoff and Baym equations. The information contained in the Green’s function is discussed. In equilibrium this leads to the Matsubara diagrammatic technique.

scholarly journals Attenuation and amplification of the transient current in nanojunctions with time-varying gate potentials

2017 ◽  
Vol 31 (14) ◽  
pp. 1750105 ◽  
Author(s):  
Eduardo C. Cuansing
Keyword(s):  
Steady State ◽  
Green's Functions ◽  
Green’S Functions ◽  
Step Function ◽  
Time Varying ◽  
Nonequilibrium Green’S Functions ◽  
Bias Potential ◽  
Gate Potential ◽  
Drain Bias ◽  
Nonequilibrium Green's Functions

We study charge transport in a source-channel-drain system with a time-varying applied gate potential acting on the channel. We calculate both the current flowing from the source into channel and out of the channel into the drain. The current is expressed in terms of nonequilibrium Green’s functions. These nonequilibrium Green’s functions can be determined from the steady-state Green’s functions and the equilibrium Green’s functions of the free leads. We find that the application of the gate potential can induce current to flow even when there is no source-drain bias potential. However, the direction of the current from the source and the current to the drain are opposite, thereby resulting in no net current flowing within the channel. When a source-drain bias potential is present, the net current flowing to the source and drain can either be attenuated or amplified depending on the sign of the applied gate potential. We also find that the response of the system to a dynamically changing gate potential is not instantaneous, i.e., a relaxation time has to pass before the current settles into a steady value. In particular, when the gate potential is in the form of a step function, the current first overshoots to a maximum value, oscillates and then settles down to a steady-state value.

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