Mesoscopic Full Counting Statistics and Exclusion models

We calculate the distribution of current fluctuations in two simple exclusion models. Although these models are classical, we recover even for small systems such as a simple or a double barrier, the same distibution of current as given by traditionnal formalisms for quantum mesoscopic conductors. Due to their simplicity, the full counting statistics in exclusion models can be reduced to the calculation of the largest eigenvalue of a matrix, the size of which is the number of internal configurations of the system. As examples, we derive the shot noise power and higher order statistics of current fluctuations (skewness, full counting statistics, ....) of various conductors, including multiple barriers, diffusive islands between tunnel barriers and diffusive media. A special attention is dedicated to the third cumulant, which experimental measurability has been demonstrated lately.Comment: Submitted to Eur. Phys. J.

Nonlocal edge state transport in the quantum spin Hall state

We present direct experimental evidence for nonlocal transport in HgTe quantum wells in the quantum spin Hall regime, in the absence of any external magnetic field. The data conclusively show that the non-dissipative quantum transport occurs through edge channels, while the contacts lead to equilibration between the counter-propagating spin states at the edge. We show that the experimental data agree quantitatively with the theory of the quantum spin Hall effect.Comment: 13 pages, 4 figure

First-Principles Study on Electron Conduction in Sodium Nanowire

We present detailed first-principles calculations of the electron-conduction properties of a three-sodium-atom nanowire suspended between semi-infinite crystalline Na(001) electrodes during its elongation. Our investigations reveal that the conductance is ~1 G0 before the nanowire breaks and only one channel with the characteristic of the $3s$ orbital of the center atom in the nanowire contributes to the electron conduction. Moreover, the channel fully opens around the Fermi level, and the behavior of the channel-current density is insensitive to the structural deformation of the nanowire. These results verify that the conductance trace as a function of the electrode spacing exhibits a flat plateau at ~1 G0 during elongation.Comment: 8 pages, 5 figure

Ground-state phase diagrams of the generalized Falicov-Kimball model with Hund coupling

Charge and spin orderings are studied on the simplest 1D and the 2D square lattice within the generalized Falicov-Kimball model with Hund coupling between localized and itinerant electrons. Using the restricted phase diagrams method (RPDM) a number of simple rules of formation of various sorts of ground state phases have been detected. In particular, relationships between density of current carriers (electrons or holes) and type of charge and magnetic arrangement has been determined. In 2D in the mixed valence regime only axial stripes (vertical or horizontal) have been found for intermediate values of the coupling constants. They are composed of ferromagnetic or antiferromagnetic chains interchanged with non-magnetic ones. For band fillings close to the half filling stripe phases oriented along one of the main diagonal direction are formed. The results suggest a possibility of tuning modulations of charge and magnetic superstructures with a change of doping.Comment: 10 pages, 6 figures; Fig. 2 slightly modified and the text adjusted accordingly, references adde