QRing – A scalable parallel software tool for quantum transport simulations in carbon nanoring

nanoring devices based on NEGF formalism and a parallel C++ / MPI / PETSc algorithm. The ability of a nanomaterial to conduct charge is essential for many nanodevice applications. While suitable nanomaterials should have acceptable electron transport properties in the absence of disorder, numerous studies have shown that disorder (including phononic or plasmonic effects) can disrupt, or even block, electric current in nanomaterials. On the other hand, some defects in graphene nanoribbons (GNRs), particularly those near the edges, seem to have negligible impact on the current. Phonons for example distort the lattice and appear as scattering centers to electrons. This leads to electrical resistance and heating. Electron-phonon scattering is also key in the understanding of positive magneto-resistance, superconductivity, Peierls instability, Raman scattering and chirality in electronic transport. Additionally, velocity renormalization, carrier lifetime corrections and dramatic reduction of high carrier mobility are known in graphene due to electron-phonon scattering with optical phonons in high fields while in the low-energy limit quasi-elastic scattering of electrons by longwavelength acoustic phonons will dominate. Another quickly expanding area of nanodevice applications with CNTs and GNRs is nanoplasmonics, where coherent electronic oscillations can be tuned via gate voltage and doping. Graphene THz devices are being created due to the strong plasmon confinement and high electron mobility in a single graphene sheet with fascinating applications in fast sensor technology. Strong exciton-plasmon coupling in semiconducting carbon nanotubes have been theoretically predicted together with scattering of surface plasmons and electrons in general, and corrections have been observed experimentally to the Dirac-like electronic dispersion in graphene. Thus, a theoretically accurate account of both electron-phonon and electronplasmon coupling in CNT and GNR based structures is of ultimate importance to properly predict the performance of these new nanoplasmonic devices. Thus, this objective aims to understand how disorder, as caused by the inelastic scattering of charge carriers on defects, phonons and plasmons, changes the current pathways, i.e., the routes electrons take while traversing the nanomaterial. The ideas of transmission eigenchannels (scattering states with well-defined transmission probabilities) and local currents (currents between two arbitrary points) will be used together to address several fundamental questions: How is current deflected by disorder, if at all? Over what length scales do phonons or plasmons perturb the current pathways? Conveniently, the nonequilibrium Green's function method described further will easily provide all quantities needed for this analysis.