ABSTRACT A Landauer formula for the current through a region of interacting electrons is derived using the nonequilibrium Keldysh formalism. The case of proportionate coupling to the left and right leads, where the formula takes an especially simple form, is studied in more detail. Two particular examples where interactions give rise to novel effects in the current are discussed: In the Kondo regime, an enhanced conductance is predicted, while a suppressed conductance is predicted for tunneling through a quantum dot in the fractional quantum Hall regime.
"[25] [57]). The non-equilibrium Green's function (NEGF), probably the most popular method, was developed in the 1990s to address transport through quantum dots [58], but since then, it has been widely applied in transport through molecular junctions [25] [57]. At its core is the division of the system into three separate regions comprising the left electrode, the right electrode, and the central region (sometimes referred to as the molecular bridge). "
[Show abstract][Hide abstract] ABSTRACT: One of the ultimate goals of molecular electronics is to create technologies
that will complement - and eventually supersede - Si-based microelectronics
technologies. To reach this goal, electronic properties that mimic at least
some of the electrical behaviors of today's semiconductor components must be
recognized and characterized. AN outstanding example for one such behavior is
negative differential conductance (NDC), in which an increase in voltage across
the device terminals results in a decrease in the electrical current passing
through the device. This overview focuses on the NDC phenomena observed in
metal-single molecule-metal junctions, and is roughly divided into two parts.
In the first part, the central experiments which demonstrate NDC in
single-molecule junctions are critically overviewed, with emphasis on the main
observations and their possible physical origins. The second part is devoted to
the theory of NDC in single-molecule junctions, where simple models are
employed to shed light on possible mechanisms leading to NDC.
"In presence of e-ph interactions inside the device region the current can generally be described by the Meir-Wingreen expression [43]. However, this formulation is often not practical to evaluate at the DFT-NEGF level. "
[Show abstract][Hide abstract] ABSTRACT: While the role of sampling of the electron momentum k in supercell calculations of the elastic electron transmission is well understood, its influence in the case of inelastic electron tunneling (IET) has not yet been systematically explored. Here we compare ab initio IET spectra of molecular monolayers in the commonly used Gamma-point approximation to rigorously k-converged results. We study four idealized molecular junctions with either alkanedithiolates or benzenedithiolates, and explore variations due to varying molecular tilt angle, density, as well as chemical identity of the monolayer. We show that the Gamma-point approximation is reasonable for a range of systems, but that a rigorous convergence is needed for accurate signal amplitudes. We also describe an approximative scheme which reduces the computational cost of the k-averaged calculation in our implementation.
Physical Review B 01/2015; 91(3). DOI:10.1103/PhysRevB.91.035434 · 3.74 Impact Factor
"One way of representing reservoirs that treats effects of memory and entanglement exactly is via the partitioning approach: large quantum systems are initially thermalized, then connected to a small system through which flows are studied, the whole being unitarily evolved. This is a formulation used in the context of quantum dots [45] [46] [47] [48] [49]. However, such reservoirs will furnish thermalized carriers only if they are ballistically transported within them. "
[Show abstract][Hide abstract] ABSTRACT: Let an infinite, homogeneous, many-body quantum system be unitarily evolved
for a long time from a state where two halves are independently thermalized.
One says that a non-equilibrium steady state emerges if there are nonzero
steady currents in the central region. In particular, their presence is a
signature of ballistic transport. We analyze the consequences of the current
observable being a conserved density; near equilibrium this is known to give
rise to linear wave propagation and a nonzero Drude peak. Using the
Lieb-Robinson bound, we derive, under a certain regularity condition, a lower
bound for the non-equilibrium steady-state current determined by equilibrium
averages. This shows and quantifies the presence of ballistic transport far
from equilibrium. The inequality suggests the definition of "nonlinear sound
velocities", which specialize to the sound velocity near equilibrium in
non-integrable models, and "generalized sound velocities", which encode
generalized Gibbs thermalization in integrable models. These are bounded by the
Lieb-Robinson velocity. The inequality also gives rise to a bound on the energy
current noise in the case of pure energy transport. We show that the inequality
is satisfied in many models where exact results are available, and that it is
saturated at one-dimensional criticality.
Nuclear Physics B 10/2014; 892. DOI:10.1016/j.nuclphysb.2015.01.007 · 3.93 Impact Factor
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