2,429 research outputs found
Heterogeneity and Disorder: Contributions of Rolf Landauer
Rolf Landauer made important contributions to many branches of science.
Within the broad area of transport in disordered media, he wrote seminal papers
on electrical conduction in macroscopically inhomogeneous materials, as well as
fundamental analyses of electron transport in quantum mechanical systems with
disorder on the atomic scale. We review here some of these contributions. We
also briefly describe some main events in his personal and scientific life.Comment: 10 pages, 3 figures; presented on the occasion when Rolf Landauer was
awarded, posthumously, the inaugural ETOPIM Medal at the ETOPIM 8 Conference,
which took place during 7--12 June, 2009 in Rethymnon, Cret
Transport in Molecular Junctions with Different Metallic Contacts
Ab initio calculations of phenyl dithiol connected to Au, Ag, Pd, and Pt
electrodes are performed using non-equilibrium Green's functions and density
functional theory. For each metal, the properties of the molecular junction are
considered both in equilibrium and under bias. In particular, we consider in
detail charge transfer, changes in the electrostatic potential, and their
subsequent effects on the IV curves through the junctions. Gold is typically
used in molecular junctions because it forms strong chemical bonds with sulfur.
We find however that Pt and Pd make better electrical contacts than Au. The
zero-bias conductance is found to be greatest for Pt, followed by Pd, Au, and
then Ag
Spectrum of Electrons in Graphene as an Alternant Macromolecule and Its Specific Features in Quantum Conductance
An exact description of electrons based on the tight-binding model of
graphene as an alternant, plane macromolecule is presented. The model molecule
can contain an arbitrary number of benzene rings and has armchair- and
zigzag-shaped edges. This suggests an instructive alternative to the most
commonly used approach, where the reference is made to the honeycomb lattice
periodic in its A and B sublattices. Several advantages of the macromolecule
model are demonstrated. The newly derived analytical relations detail our
understanding of electron nature in achiral graphene ribbons and carbon
tubes and classify these structures as quantum wires.Comment: 13 pages 8 figures, revised in line with referee's comment
Distributions of Conductance and Shot Noise and Associated Phase Transitions
For a chaotic cavity with two indentical leads each supporting N channels, we
compute analytically, for large N, the full distribution of the conductance and
the shot noise power and show that in both cases there is a central Gaussian
region flanked on both sides by non-Gaussian tails. The distribution is weakly
singular at the junction of Gaussian and non-Gaussian regimes, a direct
consequence of two phase transitions in an associated Coulomb gas problem.Comment: 5 pages, 3 figures include
New mechanism for impurity-induced step bunching
Codeposition of impurities during the growth of a vicinal surface leads to an
impurity concentration gradient on the terraces, which induces corresponding
gradients in the mobility and the chemical potential of the adatoms. Here it is
shown that the two types of gradients have opposing effects on the stability of
the surface: Step bunching can be caused by impurities which either lower the
adatom mobility, or increase the adatom chemical potential. In particular,
impurities acting as random barriers (without affecting the adatom binding)
cause step bunching, while for impurities acting as random traps the
combination of the two effects reduces to a modification of the attachment
boundary conditions at the steps. In this case attachment to descending steps,
and thus step bunching, is favored if the impurities bind adatoms more weakly
than the substrate.Comment: 7 pages, 3 figures. Substantial revisions and correction
Quantized Conductance of a Single Magnetic Atom
A single Co atom adsorbed on Cu(111) or on ferromagnetic Co islands is
contacted with non-magnetic W or ferromagnetic Ni tips in a scanning tunneling
microscope. When the Co atom bridges two non-magnetic electrodes conductances
of 2e^2/h are found. With two ferromagnetic electrodes a conductance of e^2/h
is observed which may indicate fully spin-polarized transport.Comment: 3 pages, 2 figure
Dynamic generation of orbital quasiparticle entanglement in mesoscopic conductors
We propose a scheme for dynamically creating orbitally entangled
electron-hole pairs through a time-dependent variation of the electrical
potential in a mesoscopic conductor. The time-dependent potential generates a
superposition of electron-hole pairs in two different orbital regions of the
conductor, a Mach-Zehnder interferometer in the quantum Hall regime. The
orbital entanglement is detected via violation of a Bell inequality, formulated
in terms of zero-frequency current noise. Adiabatic cycling of the potential,
both in the weak and strong amplitude limit, is considered.Comment: 4 pages, 2 figures; references update
Thermodynamical Detection of Entanglement by Maxwell's Demons
Quantum correlation, or entanglement, is now believed to be an indispensable
physical resource for certain tasks in quantum information processing, for
which classically correlated states cannot be useful. Besides information
processing, what kind of physical processes can exploit entanglement? In this
paper, we show that there is indeed a more basic relationship between
entanglement and its usefulness in thermodynamics. We derive an inequality
showing that we can extract more work out of a heat bath via entangled systems
than via classically correlated ones. We also analyze the work balance of the
process as a heat engine, in connection with the Second Law of thermodynamics.Comment: 5 pages, 4 figures. v3: a figure added, a few refs added, & typos
correcte
Hall Voltage with the Spin Hall Effect
The spin Hall effect does not generally result in a charge Hall voltage. We
predict that in systems with inhomogeneous electron density in the direction
perpendicular to main current flow, the spin Hall effect is instead accompanied
by a Hall voltage. Unlike the ordinary Hall effect, we find that this Hall
voltage is quadratic in the longitudinal electric field for a wide range of
parameters accessible experimentally. We also predict spin accumulation in the
bulk and sharp peaks of spin-Hall induced charge accumulation near the edges.
Our results can be readily tested experimentally, and would allow the
electrical measurement of the spin Hall effect in non-magnetic systems and
without injection of spin-polarized electrons
Quantum transport and momentum conserving dephasing
We study numerically the influence of momentum-conserving dephasing on the
transport in a disordered chain of scatterers. Loss of phase memory is caused
by coupling the transport channels to dephasing reservoirs. In contrast to
previously used models, the dephasing reservoirs are linked to the transport
channels between the scatterers, and momentum conserving dephasing can be
investigated. Our setup provides a model for nanosystems exhibiting conductance
quantization at higher temperatures in spite of the presence of phononic
interaction. We are able to confirm numerically some theoretical predictions.Comment: 7 pages, 4 figure
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