839 research outputs found
Quantum Transparency of Anderson Insulator Junctions: Statistics of Transmission Eigenvalues, Shot Noise, and Proximity Conductance
We investigate quantum transport through strongly disordered barriers, made
of a material with exceptionally high resistivity that behaves as an Anderson
insulator or a ``bad metal'' in the bulk, by analyzing the distribution of
Landauer transmission eigenvalues for a junction where such barrier is attached
to two clean metallic leads. We find that scaling of the transmission
eigenvalue distribution with the junction thickness (starting from the single
interface limit) always predicts a non-zero probability to find high
transmission channels even in relatively thick barriers. Using this
distribution, we compute the zero frequency shot noise power (as well as its
sample-to-sample fluctuations) and demonstrate how it provides a single number
characterization of non-trivial transmission properties of different types of
disordered barriers. The appearance of open conducting channels, whose
transmission eigenvalue is close to one, and corresponding violent mesoscopic
fluctuations of transport quantities explain at least some of the peculiar
zero-bias anomalies in the Anderson-insulator/superconductor junctions observed
in recent experiments [Phys. Rev. B {\bf 61}, 13037 (2000)]. Our findings are
also relevant for the understanding of the role of defects that can undermine
quality of thin tunnel barriers made of conventional band-insulators.Comment: 9 pages, 8 color EPS figures; one additional figure on mesoscopic
fluctuations of Fano facto
Boson-fermion unification, superstrings, and Bohmian mechanics
Bosonic and fermionic particle currents can be introduced in a more unified
way, with the cost of introducing a preferred spacetime foliation. Such a
unified treatment of bosons and fermions naturally emerges from an analogous
superstring current, showing that the preferred spacetime foliation appears
only at the level of effective field theory, not at the fundamental superstring
level. The existence of the preferred spacetime foliation allows an objective
definition of particles associated with quantum field theory in curved
spacetime. Such an objective definition of particles makes the Bohmian
interpretation of particle quantum mechanics more appealing. The superstring
current allows a consistent Bohmian interpretation of superstrings themselves,
including a Bohmian description of string creation and destruction in terms of
string splitting. The Bohmian equations of motion and the corresponding
probabilistic predictions are fully relativistic covariant and do not depend on
the preferred foliation.Comment: 30 pages, 1 figure, revised, to appear in Found. Phy
Optimizing the speed of a Josephson junction
We review the application of dynamical mean-field theory to Josephson
junctions and study how to maximize the characteristic voltage IcRn which
determines the width of a rapid single flux quantum pulse, and thereby the
operating speed in digital electronics. We study a wide class of junctions
ranging from SNS, SCmS (where Cm stands for correlated metal), SINIS (where the
insulating layer is formed from a screened dipole layer), and SNSNS structures.
Our review is focused on a survey of the physical results; the formalism has
been developed elsewhere.Comment: (36 pages, 15 figures, to appear in Int. J. Mod. Phys. B
Spin-transfer torque and spin-polarization in topological-insulator/ferromagnet vertical heterostructures
We predict an unconventional spin-transfer torque (STT) acting on the
magnetization of a free ferromagnetic (F) layer within N/TI/F vertical
heterostructures which originates from strong spin-orbit coupling (SOC) on the
surface of a three-dimensional topological insulator (TI), as well as from
charge current becoming spin-polarized in the direction of transport as it
flows from the normal metal (N) across the bulk of the TI slab. Unlike
conventional STT in symmetric F'/I/F magnetic tunnel junctions, where only the
in-plane STT component is non-zero in the linear response, both the in-plane
and perpendicular torque are sizable in N/TI/F junctions while not requiring
fixed F' layer as spin-polarizer which is advantageous for spintronic
applications. Using the nonequilibrium Born-Oppenheimer treatment of
interaction between fast conduction electrons and slow magnetization, we derive
a general Keldysh Green function-based STT formula which makes it possible to
analyze torque in the presence of SOC either in the bulk or at the interface of
the free F layer.Comment: 5 pages, 3 figures, PDFLaTe
Social Media Interactions and Online Games - Building up New Human Relationships in Danube Region
In this paper we are trying to explore possibilities of using online environment,multiplayer gaming culture and social media networks to engage people in the DanubeRegion around social, multi-cultural and environment initiatives. The Danube Region onlinecommunity could become a new cultural phenomena, technology mediated, built on humaninteractions, common interests and cultural heritage which open space for future humancenteredsocial and infrastructural design initiatives. We believe that such social mediaenvironment could also be a research playground where people form Danube Region mayexpress their needs and desires as well as to leave the trace of their behavior, significant forfurther Danube Region development
Shot Noise Probing of Magnetic Ordering in Zigzag Graphene Nanoribbons
The nonequilibrium time-dependent fluctuations of charge current have
recently emerged as a sensitive experimental tool to probe ballistic transport
through evanescent wave functions introduced into clean wide and short graphene
strips by the attached metallic electrodes. We demonstrate that such
"pseudo-diffusive" shot noise can be substantially modified in zigzag graphene
nanoribbon (ZGNR) due to the topology of its edges responsible for localized
states that facilitate ferromagnetic ordering along the edge when Coulomb
interaction is taken into account. Thus, the shot noise enhancement of
unpolarized, and even more sensitively of spin-polarized, charge currents
injected into ZGNR will act as an all-electrical and edge-sensitive probe of
such low-dimensional magnetism.Comment: 5 pages, 3 color figures; references update
Quantum mechanics: Myths and facts
A common understanding of quantum mechanics (QM) among students and practical
users is often plagued by a number of "myths", that is, widely accepted claims
on which there is not really a general consensus among experts in foundations
of QM. These myths include wave-particle duality, time-energy uncertainty
relation, fundamental randomness, the absence of measurement-independent
reality, locality of QM, nonlocality of QM, the existence of well-defined
relativistic QM, the claims that quantum field theory (QFT) solves the problems
of relativistic QM or that QFT is a theory of particles, as well as myths on
black-hole entropy. The fact is that the existence of various theoretical and
interpretational ambiguities underlying these myths does not yet allow us to
accept them as proven facts. I review the main arguments and counterarguments
lying behind these myths and conclude that QM is still a
not-yet-completely-understood theory open to further fundamental research.Comment: 51 pages, pedagogic review, revised, new references, to appear in
Found. Phy
Quantum-interference-controlled three-terminal molecular transistors based on a single ring-shaped-molecule connected to graphene nanoribbon electrodes
We study all-carbon-hydrogen molecular transistors where zigzag graphene
nanoribbons play the role of three metallic electrodes connected to a
ring-shaped 18-annulene molecule. Using the nonequilibrium Green function
formalism combined with density functional theory, recently extended to
multiterminal devices, we show that the proposed nanostructures exhibit
exponentially small transmission when the source and drain electrodes are
attached in a configuration that ensures destructive interference of electron
paths around the ring. The third electrode, functioning either as an attached
infinite-impedance voltage probe or as an "air-bridge" top gate covering half
of molecular ring, introduces dephasing that brings the transistor into the
"on" state with its transmission in the latter case approaching the maximum
limit for a single conducting channel device. The current through the latter
device can also be controlled in the far-from-equilibrium regime by applying a
gate voltage.Comment: 5 pages, 4 color figures, PDFLaTeX, slightly expanded version of the
published PRL articl
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