Nonlinear electronic transport in nanoscopic devices: nonequilibrium Green’s functions versus scattering approach

摘要

We study the nonlinear elastic quantum electronic transport properties ofnanoscopic devices using the Nonequilibrium Green's function (NEGF) method. TheGreen's function method allows us to expand the $I-V$ characteristics of agiven device to arbitrary powers of the applied voltages. By doing so, we areable to relate the NEGF method to the scattering approach, showing theirsimilarities and differences and calculate the conductance coefficients toarbitrary order. We demonstrate that the electronic current given by NEGF isgauge invariant to all orders in powers of $V$, and discuss the requirementsfor gauge invariance in the standard Density Functional Theory (DFT)implementations in molecular electronics. We also analyze the symmetries of thenonlinear conductance coefficients with respect to a magnetic field inversionand the violation of the Onsager reciprocity relations with increasingsource-drain bias.