19 research outputs found
Quantized magneto-thermoelectric transport in low-dimensional junctions
Quantization of the magneto-thermoelectric transport is studied when an
external d.c. magnetic field is applied to the C/N-knot formed as crossing
between a narrow stripe of conducting atomic monolayer C on the one hand and
metal stripe N on the other hand. The temperature gradient in C is created by
injecting the non-equilibrium electrons, holes and phonons from the heater H
thereby directing them toward the C/N-knot. A non-linear coupling between
electron states of the C/N-knot counter electrodes causes splitting of the heat
flow into several fractions owing to the Lorentz force acting in the C/N-knot
vicinity, thereby inducing the magneto-thermoelectric current in N whereas the
phonons pass and propagate along C further ahead. The heat flow along C
generates a transversal electric current in N showing a series of maximums when
dimensions of the Landau orbits and the C/N-knot match each other. It allows
observing the interplay between the quantum Hall effect and the spatial
quantization
Reversable heat flow through the carbon nanotube junctions
Microscopic mechanisms of externally controlled reversable heat flow through
the carbon nanotube junctions (NJ) are studied theoretically. Our model
suggests that the heat is transfered along the tube section by
electrons () and holes () moving ballistically in either in parallel or
in opposite directions and accelerated by the bias source-drain voltage (Peltier effect). We compute the Seebeck coefficient , electric
and thermal conductivities and find that their magnitudes
strongly depend on and . The sign reversal of
versus the sign of formerly observed experimentally is interpreted
in this work in terms of so-called chiral tunneling phenomena (Klein paradox)
Probing the intrinsic state of a one-dimensional quantum well with a photon-assisted tunneling
The photon-assisted tunneling (PAT) through a single wall carbon nanotube
quantum well (QW) under influence an external electromagnetic field for probing
of the Tomonaga Luttinger liquid (TLL) state is suggested. The elementary TLL
excitations inside the quantum well are density () and spin
() bosons. The bosons populate the quantized energy levels
and where is the interlevel spacing, is an
integer number, is the tube length, is the TLL parameter. Since the
electromagnetic field acts on the bosons only while the neutral
and bosons remain unaffected, the PAT spectroscopy
is able of identifying the levels in the QW setup. The spin
boson levels in the same QW are recognized from Zeeman
splitting when applying a d.c. magnetic field field. Basic TLL
parameters are readily extracted from the differential conductivity curves.Comment: 10 pages, 5 figure
Electromagnetic properties of graphene junctions
A resonant chiral tunneling (CT) across a graphene junction (GJ) induced by
an external electromagnetic field (EF) is studied. Modulation of the electron
and hole wavefunction phases by the external EF during the CT
processes strongly impacts the CT directional diagram. Therefore the a.c.
transport characteristics of GJs depend on the EF polarization and frequency
considerably. The GJ shows great promises for various nanoelectronic
applications working in the THz diapason.Comment: 4 pages 3 figure
Directional photoelectric current across the bilayer graphene junction
A directional photon-assisted resonant chiral tunneling through a bilayer
graphene barrier is considered. An external electromagnetic field applied to
the barrier switches the transparency in the longitudinal direction from
its steady state value T=0 to the ideal T=1 at no energy costs. The switch
happens because the a.c. field affects the phase correlation between the
electrons and holes inside the graphene barrier changing the whole angular
dependence of the chiral tunneling (directional photoelectric effect). The
suggested phenomena can be implemented in relevant experiments and in various
sub-millimeter and far-infrared optical electronic devices.Comment: 7 pages 5 figure
Charge-imbalance effects in intrinsic Josephson systems
We report on two types of experiments with intrinsic Josephson systems made
from layered superconductors which show clear evidence of nonequilibrium
effects: 1. In 2-point measurements of IV-curves in the presence of high-
frequency radiation a shift of the voltage of Shapiro steps from the canonical
value hf/(2e) has been observed. 2. In the IV-curves of double-mesa structures
an influence of the current through one mesa on the voltage measured on the
other mesa is detected. Both effects can be explained by charge-imbalance on
the superconducting layers produced by the quasi-particle current, and can be
described successfully by a recently developed theory of nonequilibrium effects
in intrinsic Josephson systems.Comment: 8pages, 9figures, submitted to Phys. Rev.
Vortex Pinning and the Non-Hermitian Mott Transition
The boson Hubbard model has been extensively studied as a model of the zero
temperature superfluid/insulator transition in Helium-4 on periodic substrates.
It can also serve as a model for vortex lines in superconductors with a
magnetic field parallel to a periodic array of columnar pins, due to a formal
analogy between the vortex lines and the statistical mechanics of quantum
bosons. When the magnetic field has a component perpendicular to the pins, this
analogy yields a non-Hermitian boson Hubbard model. At integer filling, we find
that for small transverse fields, the insulating phase is preserved, and the
transverse field is exponentially screened away from the boundaries of the
superconductor. At larger transverse fields, a ``superfluid'' phase of tilted,
entangled vortices appears. The universality class of the transition is found
to be that of vortex lines entering the Meissner phase at H_{c1}, with the
additional feature that the direction of the tilted vortices at the transition
bears a non-trivial relationship to the direction of the applied magnetic
field. The properties of the Mott Insulator and flux liquid phases with tilt
are also discussed.Comment: 20 pages, 12 figures included in text; to appear in Physical Review
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic