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We present a time-linear scaling method to simulate open and correlated quantum systems out of equilibrium. The method inherits from many-body perturbation theory the possibility to choose selectively the most relevant scattering processes in the dynamics, thereby paving the way to the real-time characterization of correlated ultrafast phenomena in quantum transport. The open system dynamics is described in terms of an embedding correlator from which the time-dependent current can be calculated using the Meir-Wingreen formula. We show how to efficiently implement our approach through a simple grafting into recently proposed time-linear Green's function methods for closed systems. Electron-electron and electron-phonon interactions can be treated on equal footing while preserving all fundametal conservation laws., Comment: 6 pages and 3 figures in the main text, 4 pages and 2 figures in the supplemental material

The nonequilibrium excitonic insulator (NEQ-EI) is an excited state of matter characterized by a finite density of coherent excitons and a time-dependent macroscopic polarization. The stability of this exciton superfluid as the density grows is jeopardized by the increased screening efficiency of the looser excitons. In this work we put forward a Hartree plus Screened Exchange HSEX scheme to predict the critical density at which the transition toward a free electron-hole plasma occurs. The dielectric function is calculated self-consistently using the NEQ-EI polarization and found to vanish in the long-wavelength limit. This property makes the exciton superfluid stable up to relatively high densities. Numerical results for the MoS$_{2}$ monolayers indicate that the NEQ-EI phase survives up to densities of the order of $10^{12}\mathrm{cm}^{-2}$., Comment: 8 pages, 4 figures

We study the combined effects of electron-phonon coupling and dot-lead repulsion in the transport properties of the Anderson-Holstein model. We employ a recently proposed nonperturbative method to calculate the transient response of the system. By varying the initial conditions for the time propagation the current exhibits transient oscillations of different nature. We are able to disentangle two dynamical processes, namely the local charge rearrangement due to the dot-lead contacting and the establishment of the nonequilbrium many-body state due to the application of the external bias. These processes involve either Franck-Condon excitations or transitions between the resonant level and the Fermi energy of the leads., Comment: 6 pages, 6 figures

Screening effects in nanoscale junctions with strong electron-phonon coupling open new physical scenarios. We propose an accurate many-body approach to deal with the simultaneous occurrence of the Franck-Condon blockade and the screening-induced enhancement of the polaron mobility. We derive a transparent analytic expression for the electrical current: transient and steady-state features are directly interpreted and explained. Moreover, the interplay between phononic and electronic excitations gives rise to a novel mechanism of negative differential conductance. Experimental setup to observe this phenomenon are discussed., 5 pages, 5 figures

Controlling the dynamics of Majorana fermions (MF) subject to time-varying driving fields is of fundamental importance for the practical realization of topological quantum computing. In this work we study how it is possible to dynamically generate and maintain the topological phase in one-dimensional superconducting nanowires after the temporal variation of the Hamiltonian parameters. Remarkably we show that for a sudden quench the system can never relax towards a state exhibiting fully developed MF, independently of the initial and final Hamiltonians. Only for sufficiently slow protocols the system behaves adiabatically, and the topological phase can be reached. Finally we address the crucial question of how "adiabatic" a protocol must be in order to manipulate the MF inside the topological phase without deteriorating their Majorana character., 5 pages, 4 eps figures

The effects of long-range interactions in quantum transport are still largely unexplored, mainly due to the difficulty of devising efficient embedding schemes. In this work we present a substantial progress in the interacting resonant level model by reducing the problem to the solution of Kadanoff-Baym-like equations with a correlated embedding self-energy. The method allows us to deal with short- and long-range interactions and is applicable from the transient to the steady-state regime. Furthermore, memory effects are consistently incorporated and the results are not plagued by negative densities or non-conservation of the electric charge. We employ the method to calculate densities and currents with long-range interactions appropriate to low-dimensional leads, and show the occurrence of a jamming effect which drastically reduces the screening time and suppresses the zero-bias conductance. None of these effects are captured by short-range dot-lead interactions., Comment: 5 pages, 4 figures

We present a dynamical theory of the Auger decay in one-dimensional (1D) metals described by the Tomonaga-Luttinger model. An analytic expression of the Auger current is derived in the framework of the 1-step approach, where the finite lifetime of the initial core-hole and the core-valence interaction are taken into account. This allows to capture typical dynamical features like the shake-down effect, in which the Auger spectrum shows a non-vanishing weight above the 2-step high-energy threshold. The obtained results give also a hint to understand the sizable suppression of Auger spectral weight closed to the Fermi energy recently observed in carbon nanotubes with respect to graphite., 6 pages, 2 figures. To appear in Phys. Rev. B

We address the question of how small can the quasiparticle decay rate be at low energies in undoped graphene, where kinematical constraints are known to prevent the decay into particle-hole excitations. For this purpose, we study the renormalization of the phonon dispersion by many-body effects, which turns out to be very strong in the case of the out-of-plane phonons at the K point of the spectrum. We show that these evolve into a branch of very soft modes that provide the relevant channel for quasiparticle decay, at energies below the scale of the optical phonon modes. In this regime, we find that the decay rate is proportional to the cube of the quasiparticle energy. This implies that a crossover should be observed in transport properties from the linear dependence characteristic of the high-energy regime to the much slower decay rate due to the soft phonon modes., Comment: 5 pages, 1 figure

We investigate the effects of a transverse magnetic field on the transport properties of carbon nanotubes, making use of a long-wavelength description in terms of Dirac fermion fields. For values of the magnetic length smaller than the nanotube radius, we observe that the electronic states organize into incipient Landau subbands, with a highly degenerate level at zero energy. We show that only the states in dispersive branches, localized at the flanks of the nanotube, are able to transport current in the longitudinal direction. This is at the origin of the quantization of the Hall conductivity, that turns out to be given by even multiples of 2 e^2 /h. We also analyze the effects of the electron-electron interaction, showing that the magnetic field induces a suppression of the electronic correlations, reflected in particular in the enhancement of the tunneling density of states near the Fermi level., Comment: 4 pages, REVTeX, submitted to PRL, corrected typos