Dmitry Golubev

Side‐Gated Transport in Focused‐Ion‐Beam‐Fabricated Multilayered Graphene Nanoribbons

In this Letter, we present the patterning, exfoliation and micromanipulation of thin graphitic discs which are subsequently connected and patterned into sub-100nm wide ribbons with a resist-free process using Focused Ion Beam (FIB) lithography and deposition. The electronic transport properties of the double side-gated nanoribbons are then investigated down to 40 K and interpreted with a simple model of 1D array of tunnelling junctions.

Bidirectional Single-Electron Counting and the Fluctuation Theorem

We investigate theoretically and experimentally the full counting statistics of bidirectional singleelectron tunneling through a double quantum dot in a GaAs/GaAlAs heterostructure and compare with predictions of the fluctuation theorem (FT) for Markovian stochastic processes. We observe that the quantum point contact electrometer used to study the transport induces nonequilibrium shot noise and dot-level fluctuations and strongly modifies the tunneling statistics. As a result, the FT appears to be violated. We show that it is satisfied if the back-action of the electrometer is taken into account, and we provide a quantitative estimate of this effect. PACS numbers: 73.23.-b,73.23.Hk,72.70.+m,05.70.Ln According to the second law of thermodynamics, the entropy of a macroscopic system driven out of equilibrium increases with time until equilibrium is reached. Thus the dynamics of such a system is irreversible. In contrast, for a mesoscopic system performing a random trajectory in phase space and measured during a sufficiently short time, the entropy may either increase or decrease. The ‘Fluctuation Theorem’ (FT), which relies only on the microreversiblity of the underlying equation of motion, states that the probability distribution P�(�S) for processes increasing or decreasing the en= (�)=  

Cooper Pair Splitting by Means of Graphene Quantum Dots

A split Cooper pair is a natural source for entangled electrons which is a basic ingredient for quantum information in the solid state. We report an experiment on a superconductor-graphene double quantum dot (QD) system, in which we observe Cooper pair splitting (CPS) up to a CPS efficiency of ∼10%. With bias on both QDs, we are able to detect a positive conductance correlation across the two distinctly decoupled QDs. Furthermore, with bias only on one QD, CPS and elastic cotunneling can be distinguished by tuning the energy levels of the QDs to be asymmetric or symmetric with respect to the Fermi level in the superconductor.

Enhancing the Molecular Signature in Molecule-Nanoparticle Networks Via Inelastic Cotunneling

Charge transport in networks of nanoparticles linked by molecular spacers is investigated. Remarkably, in the regime where cotunneling dominates, the molecular signature of a device is strongly enhanced. We demonstrate that the resistance ratio of identical networks with different molecular spacers increases dramatically, from an initial value of 50 up to 10(5) , upon entering the cotunneling regime. Our work shows that intrinsic molecular properties can be amplified through nanoscale engineering.

Irreversibility on the Level of Single-Electron Tunneling

We present a low-temperature experimental test of the fluctuation theorem for electron transport through a double quantum dot. The rare entropy-consuming system trajectories are detected in the form of single charges flowing against the source-drain bias by using time-resolved charge detection with a quantum point contact. We find that these trajectories appear with a frequency that agrees with the theoretical predictions even under strong nonequilibrium conditions, when the finite bandwidth of the charge detection is taken into account. The second law of thermodynamics states that a macroscopic system out of thermal equilibrium will irreversibly move toward equilibrium driven by a steady increase of its entropy. This macroscopic irreversibility occurs despite the time-reversal symmetry of the underlying microscopic equations of motion. Also, a microscopic system will undergo an irreversible evolution on a long time scale, but, over a sufficiently short observation time � , both entropy-producing trajectories as well as their timereversed entropy-consuming counterparts occur. It is only because of the statistics of these occurrences that a longterm irreversible evolution is established. This phenomenon is described by the fluctuation theorem [1,2]. Irrespective of the description of the trajectories being system-specific, the fluctuation theorem (FT) relates the probabilities P� ð� SÞ for processes that change the entropy

Fully gapped superconductivity in a nanometre-size YBa2Cu3O7-[delta] island enhanced by a magnetic field

The symmetry of Cooper pairs is central to constructing a superconducting state. The demonstration of a d(x²-y²)-wave order parameter with nodes represented a breakthrough for high critical temperature superconductors (HTSs). However, despite this fundamental discovery, the origin of superconductivity remains elusive, raising the question of whether something is missing from the global picture. Deviations from d(x²-y²)-wave symmetry, such as an imaginary admixture d(x²-y²)+ is (or id(xy)), predict a ground state with unconventional properties exhibiting a full superconducting gap and time reversal symmetry breaking. The existence of such a state, until now highly controversial, can be proved by highly sensitive measurements of the excitation spectrum. Here, we present a spectroscopic technique based on an HTS nanoscale device that allows an unprecedented energy resolution thanks to Coulomb blockade effects, a regime practically inaccessible in these materials previously. We find that the energy required to add an extra electron depends on the parity (odd/even) of the excess electrons on the island and increases with magnetic field. This is inconsistent with a pure d(x²-y²)-wave symmetry and demonstrates a complex order parameter component that needs to be incorporated into any theoretical model of HTS.

Strong electron tunneling through mesoscopic metallic grains

We describe electron transport through small metallic grains with Coulomb blockade effects beyond the perturbative regime. For this purpose we study the real-time evolution of the reduced density matrix of the system. In the first part of the paper we present a diagrammatic expansion for not too high junction conductance,

On the concept of an optimal hot-electron bolometer with NIS tunnel junctions

h/4{\ensuremath{\pi}}^{2}{e}^{2}{R}_{t}\ensuremath{\lesssim}1,

Heat transport through a Josephson junction

in a basis of charge states. Quantum fluctuations renormalize system parameters and lead to finite lifetime broadening in the gate-voltage-dependent differential conductance. We derive analytic results for the spectral density and the conductance in the limit where only two charge states play a role. In the second part of the paper we consider junctions with large conductance,

Full counting statistics of interacting electrons

{h/4e}^{2}{R}_{t}\ensuremath{\gtrsim}1.