4 Search Results

Here, we theoretically investigate the two-photon absorption signals of a three-band (g, e, f) system diagonally coupled to an over-damped Brownian oscillator bath, which induces random Gaussian modulations of energy levels with an arbitrary degree of correlation. For fast modulation, extra 2ω_eg and 2ω_fe peaks may obscure the g–f transitions in the classical two-photon absorption (CTPA) spectra for nearly resonant e states. These peaks arise from one-photon resonant g–e or e–f transitions. In the slow modulation limit, these peaks vanish because of the short tails of the Gaussian line shape. CTPA strongly depends on the correlations between energy fluctuations. Inmore » entangled two-photon absorption, the extra peaks are eliminated because of the broad one-photon but narrow two-photon spectrum of the twin photons. The variation of the coherences between f states with the correlation between energy fluctuations is explored.« less

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We consider the effects of strong light-matter interaction on electronic friction in molecular junctions within the generic model of a single molecule nanocavity junction. Results of the Hubbard nonequilibrium Green function (NEGF) simulations are compared with mean-field NEGF and generalized Head-Gordon and Tully (HGT) approaches. Mean-field NEGF is shown to fail qualitatively at strong intrasystem interactions, while accuracy of the generalized HGT results is restricted to situations of well separated intramolecular excitations when bath induced coherences are negligible. Numerical results show effects of bias and cavity mode pumping on electronic friction. Here, we demonstrate nonmonotonic behavior of the friction onmore » the bias and intensity of the pumping field and indicate possibility of engineering friction control in single molecule junctions.« less

Here, we introduce diagrammatic technique for Hubbard nonequilibrium Green functions. The formulation is an extension of equilibrium considerations for strongly correlated lattice models to description of current carrying molecular junctions. Within the technique intra-system interactions are taken into account exactly, while molecular coupling to contacts is used as a small parameter in perturbative expansion. We demonstrate the viability of the approach with numerical simulations for a generic junction model of quantum dot coupled to two electron reservoirs.