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 ${\cal T}$ by electrons ($e$) and holes ($h$) moving ballistically in either in parallel or in opposite directions and accelerated by the bias source-drain voltage $V_{\rm SD}$ (Peltier effect). We compute the Seebeck coefficient $\alpha$, electric $\sigma$ and thermal $\kappa$ conductivities and find that their magnitudes strongly depend on $V_{\rm SD}$ and $V_{\rm G}$. The sign reversal of $\alpha$ versus the sign of $V_{\rm G}$ formerly observed experimentally is interpreted in this work in terms of so-called chiral tunneling phenomena (Klein paradox)

Heat to Electricity Conversion by a Graphene Stripe with Heavy Chiral Fermions

A conversion of thermal energy into electricity is considered in the electrically polarized graphene stripes with zigzag edges where the heavy chiral fermion (HCF) states are formed. The stripes are characterized by a high electric conductance Ge and by a significant Seebeck coefficient S. The electric current in the stripes is induced due to a non-equilibrium thermal injection of "hot" electrons. This thermoelectric generation process might be utilized for building of thermoelectric generators with an exceptionally high figure of merit Z{\delta}T \simeq 100 >> 1 and with an appreciable electric power densities \sim 1 MW/cm2.Comment: 8 pages, 3 figure

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 ($\rho_{\pm}$) and spin ($\sigma_{\pm}$) bosons. The bosons populate the quantized energy levels $\epsilon^{\rho +}_n =\Delta n/ g$ and $\epsilon^{\rho -(\sigma \pm)}_n = \Delta n$ where $\Delta = h v_F /L$ is the interlevel spacing, $n$ is an integer number, $L$ is the tube length, $g$ is the TLL parameter. Since the electromagnetic field acts on the $\rho_{+}$ bosons only while the neutral $\rho_{-}$ and $\sigma_{\pm}$ bosons remain unaffected, the PAT spectroscopy is able of identifying the $\rho_{+}$ levels in the QW setup. The spin $\epsilon_n^{\sigma+}$ boson levels in the same QW are recognized from Zeeman splitting when applying a d.c. magnetic field $H \neq 0$ 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 $\varphi$ 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 $T$ 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

Collective Dynamics of Josephson Vortices in Intrinsic Josephson Junctions :Exploration of In-phase Locked Superradiant Vortex Flow States

In order to clarify the ``superradiant'' conditions for the moving Josephson vortices to excite in-phase AC electromagnetic fields over all junctions, we perform large scale simulations of realistic dimensions for intrinsic Josephson junctions under the layer parallel magnetic field. Three clear step-like structures in the I-V curve are observed above a certain high field ($H > 1T$ in the present simulations), at which we find structural transitions in the moving flux-line lattice. The Josephson vortex flow states are accordingly classified into four regions (region I $\sim$ IV with increasing current), in each of which the power spectrum for the electric field oscillations at the sample edge are measured and typical snapshots for Josephson vortex configurations are displayed. Among the four regions, especially in the region III, an in-phase rectangular vortex lattice flow state emerges and the power spectrum shows remarkably sharp peak structure, i.e., superradiant state. Comparison of the simulation results with an eigenmode analysis for the transverse propagating Josephson plasma oscillations reveals that the resonances between Josephson vortex flow states and some of the eigenmodes are responsible for the clear flux lattice structural transitions. Furthermore, the theoretical analysis clarifies that the width of the superradiant state region in the I-V characteristics enlarges with decreasing both the superconducting and insulating layer thickness.Comment: 8 pages, Revtex, 7 figures; figure arrangements improved. no changes in tex

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

In-plane fluxon in layered superconductors with arbitrary number of layers

I derive an approximate analytic solution for the in-plane vortex (fluxon) in layered superconductors and stacked Josephson junctions (SJJ's) with arbitrary number of layers. The validity of the solution is verified by numerical simulation. It is shown that in SJJ's with large number of thin layers, phase/current and magnetic field of the fluxon are decoupled from each other. The variation of phase/current is confined within the Josephson penetration depth, $\lambda_J$, along the layers, while magnetic field decays at the effective London penetration depth, $\lambda_c \gg \lambda_J$. For comparison with real high-$T_c$ superconducting samples, large scale numerical simulations with up to 600 SJJ's and with in-plane length up to 4000 $\lambda_J$%, are presented. It is shown, that the most striking feature of the fluxon is a Josephson core, manifesting itself as a sharp peak in magnetic induction at the fluxon center.Comment: 4 pages, 4 figures. Was presented in part at the First Euroconference on Vortex Matter in Superconductors (Crete, September 1999

Transport Through Andreev Bound States in a Graphene Quantum Dot

Andreev reflection-where an electron in a normal metal backscatters off a superconductor into a hole-forms the basis of low energy transport through superconducting junctions. Andreev reflection in confined regions gives rise to discrete Andreev bound states (ABS), which can carry a supercurrent and have recently been proposed as the basis of qubits [1-3]. Although signatures of Andreev reflection and bound states in conductance have been widely reported [4], it has been difficult to directly probe individual ABS. Here, we report transport measurements of sharp, gate-tunable ABS formed in a superconductor-quantum dot (QD)-normal system, which incorporates graphene. The QD exists in the graphene under the superconducting contact, due to a work-function mismatch [5, 6]. The ABS form when the discrete QD levels are proximity coupled to the superconducting contact. Due to the low density of states of graphene and the sensitivity of the QD levels to an applied gate voltage, the ABS spectra are narrow, can be tuned to zero energy via gate voltage, and show a striking pattern in transport measurements.Comment: 25 Pages, included SO