Electron Transport in Granular Metals

We consider thermodynamic and transport properties of a long granular array with strongly connected grains (inter-grain conductance g>>1.) We find that the system exhibits activated behavior of conductance and thermodynamic density of states ~exp(-T*/T) where the gap, T*, is parametrically larger than the energy at which conventional perturbation theory breaks down. The scale T* represents energy needed to create a long single-electron charge soliton propagating through the array.Comment: 4 pages, 1 figur

Electron transport in disordered graphene

We study electron transport properties of a monoatomic graphite layer (graphene) with different types of disorder. We show that the transport properties of the system depend strongly on the character of disorder. Away from half filling, the concentration dependence of conductivity is linear in the case of strong scatterers, in line with recent experimental observations, and logarithmic for weak scatterers. At half filling the conductivity is of the order of e^2/h if the randomness preserves one of the chiral symmetries of the clean Hamiltonian; otherwise, the conductivity is strongly affected by localization effects.Comment: 21 pages, 9 figure

Electron Transport in Nanogranular Ferromagnets

We study electronic transport properties of ferromagnetic nanoparticle arrays and nanodomain materials near the Curie temperature in the limit of weak coupling between the grains. We calculate the conductivity in the Ohmic and non-Ohmic regimes and estimate the magnetoresistance jump in the resistivity at the transition temperature. The results are applicable for many emerging materials, including artificially self-assembled nanoparticle arrays and a certain class of manganites, where localization effects within the clusters can be neglected.Comment: 4 pages, 2 figure

Single-Molecule Junction Conductance through Diaminoacenes

The study of electron transport through single molecules is essential to the development of molecular electronics. Indeed, trends in electronic conductance through organic nanowires have emerged with the increasing reliability of electron transport measurements at the single-molecule level. Experimental and theoretical work has shown that tunneling distance, HOMO-LUMO gap and molecular conformation influence electron transport in both saturated and pi-conjugated nanowires. However, there is relatively little experimental data on electron transport through fused aromatic rings. Here we show using diaminoacenes that conductivity depends not only on the number of fused aromatic rings in the molecule, which defines the molecular HOMO-LUMO gap, but also on the position of the amino groups on the rings. Specifically, we find that conductance is highest with minimal disruption of aromaticity in fused aromatic nanowires.Comment: 2 pages, 3 figure

Inelastic electron transport in granular arrays

Transport properties of granular systems are governed by Coulomb blockade effects caused by the discreteness of the electron charge. We show that, in the limit of vanishing mean level spacing on the grains, the low-temperature behavior of 1d and 2d arrays is insulating at any inter-grain coupling (characterized by a dimensionless conductance g.) In 2d and g>>1, there is a sharp Berezinskii-Kosterlitz-Thouless crossover to the conducting phase at a certain temperature, T_{BKT}. These results are obtained by applying an instanton analysis to map the conventional `phase' description of granular arrays onto the dual `charge' representation.Comment: 24 pages, 8 figure