Electronic friction in interacting systems

We consider effects of strong light-matter interaction on electronic friction in molecular junctions within generic model of single molecule nano cavity junction. Results of the Hubbard NEGF simulations are compared with mean-field NEGF and generalized Head-Gordon and Tully approaches. Mean-field NEGF is shown to fail qualitatively at strong intra-system interactions, while accuracy of the generalized Head-Gordon and Tully results is restricted to situations of well separated intra-molecular excitations, when bath induced coherences are negligible. Numerical results show effects of bias and cavity mode pumping on electronic friction. We demonstrate non-monotonic behavior of the friction on the bias and intensity of the pumping field and indicate possibility of engineering friction control in single molecule junctions.Comment: 19 pages, 4 figure

Current-induced forces for nonadiabatic molecular dynamics

We present general first principles derivation of expression for current-induced forces. The expression is applicable in non-equilibrium molecular systems with arbitrary intra-molecular interactions and for any electron-nuclei coupling. It provides a controlled consistent way to account for quantum effects of nuclear motion, accounts for electronic non-Markov character of the friction tensor, and opens way to treatments beyond strictly adiabatic approximation. We show connection of the expression with previous studies, and discuss effective ways to evaluate the friction tensor.Comment: 6 pages, 3 figure

Control and enhancement of single-molecule electroluminescence through strong light-matter coupling

The energetic positions of molecular electronic states at molecule/electrode interfaces are crucial factors for determining the transport and optoelectronic properties of molecular junctions. Strong light--matter coupling offers a potential for manipulating these factors, enabling to boost in the efficiency and versatility of these junctions. Here, we investigate electroluminescence from single-molecule junctions in which the molecule is strongly coupled with the vacuum electromagnetic field in a plasmonic nanocavity. We demonstrate an improvement in the electroluminescence efficiency by employing the strong light--matter coupling in conjunction with the characteristic feature of single-molecule junctions to selectively control the formation of the lowest-energy excited state. The mechanism of efficiency improvement is discussed based on the energetic position and composition of the formed polaritonic states. Our findings indicate the possibility to manipulate optoelectronic conversion in molecular junctions by strong light--matter coupling and contribute to providing design principles for developing efficient molecular optoelectronic devices

Towards Noise Simulation in Interacting Nonequilibrium Systems Strongly Coupled to Baths

Progress in experimental techniques at nanoscale made measurements of noise in molecular junctions possible. These data are important source of information not accessible through average flux measurements. Emergence of optoelectronics, recently shown possibility of strong light-matter couplings, and developments in the field of quantum thermodynamics are making counting statistics measurements of even higher importance. Theoretical methods for noise evaluation in first principles simulations can be roughly divided into approaches applicable in the case of weak intra-system interactions, and those treating strong interactions for systems weakly coupled to baths. We argue that due to structure of its diagrammatic expansion and the fact of utilizing many-body states as a basis of its formulation recently introduced nonequilibrium Hubbard Green functions formulation is a relatively inexpensive method suitable for evaluation of noise characteristics in first principles simulations over wide range of parameters. We illustrate viability of the approach by simulations of noise and noise spectrum within generic models for non-, weakly and strongly interacting systems. Results of the simulations are compared to exact data (where available) and to simulations performed within approaches best suited for each of the three parameter regimes.Comment: 19 pages, 5 figure