Electron-electron interactions in the conductivity of graphene

The effect of electron-electron interaction on the low-temperature conductivity of graphene is investigated experimentally. Unlike in other two-dimensional systems, the electron-electron interaction correction in graphene is sensitive to the details of disorder. A new temperature regime of the interaction correction is observed where quantum interference is suppressed by intra-valley scattering. We determine the value of the interaction parameter, F_0 ~ -0.1, and show that its small value is due to the chiral nature of interacting electrons.Comment: 4 pages, 4 figures, 1 tabl

Coherent Particle Transfer in an On-Demand Single-Electron Source

Coherent electron transfer from a localized state trapped in a quantum dot into a ballistic conductor, taking place in on-demand electron sources, in general may result in excitation of particle-hole pairs. We consider a simple model for these effects, involving a resonance level with time-dependent energy, and derive Floquet scattering matrix describing inelastic transitions of particles in the Fermi sea. We find that, as the resonance level is driven through the Fermi level, particle transfer may take place completely without particle-hole excitations for certain driving protocols. In particular, such noiseless transfer occurs when the level moves with constant rapidity, its energy changing linearly with time. A detection scheme for studying the coherence of particle transfer is proposed.Comment: 5 pages, 3 figures. Updated introduction, Fig. 1, and reference

Counterintuitive transitions in the multistate Landau-Zener problem with linear level crossings

We generalize the Brundobler-Elser hypothesis in the multistate Landau-Zener problem to the case when instead of a state with the highest slope of the diabatic energy level there is a band of states with an arbitrary number of parallel levels having the same slope. We argue that the probabilities of counterintuitive transitions among such states are exactly zero.Comment: 9 pages, 5 figure

Re-entrant localization of single particle transport in disordered Andreev wires

We study effects of disorder on the low energy single particle transport in a normal wire surrounded by a superconductor. We show that the heat conductance includes the Andreev diffusion decreasing with increase in the mean free path $\ell$ and the diffusive drift produced by a small particle-hole asymmetry, which increases with increasing $\ell$. The conductance thus has a minimum as a function of $\ell$ which leads to a peculiar re-entrant localization as a function of the mean free path.Comment: 4 pages, 2 figure

Millikelvin de Haas-van Alphen and magnetotransport studies of graphite

Copyright © 2011 American Physical SocietyRecent studies of the electronic properties of graphite have produced conflicting results regarding the positions of the different carrier types within the Brillouin zone, and the possible presence of Dirac fermions. In this paper we report a comprehensive study of the de Haas–van Alphen, Shubnikov–de Haas, and Hall effects in a sample of highly orientated pyrolytic graphite, at temperatures in the range 30 mK to 4 K and magnetic fields up to 12 T. The transport measurements confirm the Brillouin-zone locations of the different carrier types assigned by Schroeder, Dresselhaus and Javan Phys. Rev. Lett. 20 1292 (1968): electrons are at the K point, and holes are near the H points. We extract the cyclotron masses and scattering times for both carrier types from the temperature- and magnetic-field-dependences of the magneto-oscillations. Our results indicate that the holes experience stronger scattering and hence have lower mobility than the electrons. We utilize phase-frequency analysis and intercept analysis of the 1/B positions of magneto-oscillation extrema to identify the nature of the carriers in graphite, whether they are Dirac or normal (Schrödinger) fermions. These analyses indicate normal holes and electrons of indeterminate natur

Observation of macroscopic Landau-Zener transitions in a superconducting device

A two-level system traversing a level anticrossing has a small probability to make a so-called Landau-Zener (LZ) transition between its energy bands, in deviation from simple adiabatic evolution. This effect takes on renewed relevance due to the observation of quantum coherence in superconducting qubits (macroscopic "Schrodinger cat" devices). We report an observation of LZ transitions in an Al three-junction qubit coupled to a Nb resonant tank circuit.Comment: REVTeX4, 4pp., 4 EPS figures. v2: clarifications added; final, to appear in EP

Experiments on the Fermi to Tomonaga-Luttinger liquid transition in quasi-1D systems

We present experimental results on the tunneling into the edge of a two dimensional electron gas (2DEG) obtained with GaAs/AlGaAs cleaved edge overgrown structures. The electronic properties of the edge of these systems can be described by a one-dimensional chiral Tomonaga-Luttinger liquid when the filling factor of the 2DEG is very small. Here we focus on the region where the Tomonaga-Luttinger liquid breaks down to form a standard Fermi liquid close to $\nu=1$ and show that we recover a universal curve, which describes all existing data.Comment: 5 pages, localisation 2002, conference proceeding

Quantum theory of electromechanical noise and momentum transfer statistics

A quantum mechanical theory is developed for the statistics of momentum transferred to the lattice by conduction electrons. Results for the electromechanical noise power in the semiclassical diffusive transport regime agree with a recent theory based on the Boltzmann-Langevin equation. All moments of the transferred momentum are calculated for a single-channel conductor with a localized scatterer, and compared with the known statistics of transmitted charge.Comment: 10 pages, 2 figure

On gauge-invariant Green function in 2+1 dimensional QED

Both the gauge-invariant fermion Green function and gauge-dependent conventional Green function in $2+1$ dimensional QED are studied in the large $N$ limit. In temporal gauge, the infra-red divergence of gauge-dependent Green function is found to be regulariable, the anomalous dimension is found to be $\eta= \frac{64}{3 \pi^{2} N}$. This anomalous dimension was argued to be the same as that of gauge-invariant Green function. However, in Coulomb gauge, the infra-red divergence of the gauge-dependent Green function is found to be un-regulariable, anomalous dimension is even not defined, but the infra-red divergence is shown to be cancelled in any gauge-invariant physical quantities. The gauge-invariant Green function is also studied directly in Lorentz covariant gauge and the anomalous dimension is found to be the same as that calculated in temporal gauge.Comment: 8 pages, 6 figures, to appear in Phys. Rev.

Quantum and classical confinement of resonant states in a trilayer graphene Fabry-Pérot interferometer

The advent of few-layer graphene has given rise to a new family of two-dimensional systems with emergent electronic properties governed by relativistic quantum mechanics. The multiple carbon sublattices endow the electronic wavefunctions with pseudospin, a lattice analogue of the relativistic electron spin, whereas the multilayer structure leads to electric-field-effect tunable electronic bands. Here we use these properties to realize giant conductance oscillations in ballistic trilayer graphene Fabry-Pérot interferometers, which result from phase coherent transport through resonant bound states beneath an electrostatic barrier. We confine these states by selectively decoupling them from the leads, resulting in transport via non-resonant states and suppression of the giant oscillations. The confinement is achieved both classically, by manipulating quasiparticle momenta with a magnetic field, and quantum mechanically, by locally varying the pseudospin character of the carrier wavefunctions. Our results illustrate the unique potential of trilayer graphene as a versatile platform for electron optics and pseudospintronics.United States. Office of Naval Research (GATE MURI)National Science Foundation (U.S.) (Career Award DMR-0845287)Conselho Nacional de Pesquisas (Brazil