Vertical magneto-tunneling through a quantum dot and the density of states of small electronic systems

One-electron tunneling through a quantum dot with a strong magnetic field in the direction of the current is studied. The linear magneto-conductance is computed for a model parabolic dot with seven electrons in the intermediate states and for different values of the magnetic field. It is shown that the dot density of states at low excitation energies can be extracted from a precise measurement of the conductance at the upper edge of the Coulomb blockade diamond. We parametrized the density of states with a single ``temperature'' parameter (in the so called ``constant temperature approximation''), and found that this parameter depends very weakly on the magnetic field.Comment: Accepted in Physica

Full counting statistics for SU(N) impurity Anderson model

We analyze the full counting statistics of a multiorbital Kondo effect in a quantum dotwith the SU(N) symmetry in the framework of the renormalized perturbation theory. The current probability distribution function is calculated for an arbitrary dot-site Coulomb repulsion $U$ in the particle-hole symmetric case. The resulting cumulant up to the leading nonlinear term of applied bias voltages indicates two types of electron transfer, respectively carrying charge $e$ and $2e$, with different $N$-dependences. The cross correlation between different orbital currents shows exponential enhancement with respect to $U$, which directly addresses formation of the orbital-singlet state.Comment: 1 figure, 1 table, 5 page

Bosonization approach to the edge reconstruction of two dimentional electron systems in a quantum dot

We consider the edge reconstruction of electrons in a two dimensional harmonic trap under a strong magnetic field. In this system the edge reconstruction occurs as a result of competition between electron-electron interaction and confining potential. To describe it, we develop a bosonization scheme for two dimensional electron systems. With this method we obtain the excitation spectrum and demonstrate that the edge reconstruction occurs when the value of the magnetic field reaches a critical value. We also show that the edge reconstruction depends on the number of electrons. Additionally, we calculate the third order terms of bosons in Hamiltonian and examine the effect of those terms with a perturbation theory.Comment: 5pages, 6figure

Full counting statistics for orbital-degenerate impurity Anderson model with Hund's rule exchange coupling

We study non-equilibrium current fluctuations through a quantum dot, which includes a ferromagnetic Hund's rule coupling $J$, in the low-energy Fermi liquid regime using the renormalized perturbation theory. The resulting cumulant for the current distribution in the particle-hole symmetric case, shows that spin-triplet and spin-singlet pairs of quasiparticles are formed in the current due to the Hund's rule coupling and these pairs enhance the current fluctuations. In the fully screened higher-spin Kondo limit, the Fano factor takes a value $F_b = (9M+6)/ (5M+4)$ determined by the orbital degeneracy $M$. We also investigate crossover between the small and large $J$ limits in the two-orbital case M=2, using the numerical renormalization group approach.Comment: 5 pages, 3 figure

Double-gated graphene-based devices

We discuss transport through double gated single and few layer graphene devices. This kind of device configuration has been used to investigate the modulation of the energy band structure through the application of an external perpendicular electric field, a unique property of few layer graphene systems. Here we discuss technological details that are important for the fabrication of top gated structures, based on electron-gun evaporation of SiO$_2$. We perform a statistical study that demonstrates how --contrary to expectations-- the breakdown field of electron-gun evaporated thin SiO$_2$ films is comparable to that of thermally grown oxide layers. We find that a high breakdown field can be achieved in evaporated SiO$_2$ only if the oxide deposition is directly followed by the metallization of the top electrodes, without exposure to air of the SiO$_2$ layer.Comment: Replaced with revised version. To appear on New Journal of Physic