Vadim Cheianov

The Focusing of Electron Flow and a Veselago Lens in Graphene p-n Junctions.

The focusing of electric current by a single p-n junction in graphene is theoretically predicted. Precise focusing may be achieved by fine-tuning the densities of carriers on the n- and p-sides of the junction to equal values. This finding may be useful for the engineering of electronic lenses and focused beam splitters using gate-controlled n-p-n junctions in graphene-based transistors.The focusing of electric current by a single p-n junction in graphene is predicted. We show that precise focusing can be achieved by fine-tuning the densities of carriers on the nand p-sides of the junction to equal values, whereas the current distribution in junctions with different densities resembles caustics in optics. This finding can be utilized in the engineering of electronic lenses and focused beam-splitters using gate-controlled n-p-n junctions in graphene-based transistors. Physics Department, Lancaster University, Lancaster LA1 4YB, UK Physics Department, Columbia University, 538 West 120th Street, New York, NY 10027, USA NEC-Laboratories America, 4 Independence Way, Princeton, NJ 085540, USA

Selective transmission of Dirac electrons and ballistic magnetoresistance of n-p junctions in graphene

We show that an electrostatically created n-p junction separating the electron and hole gas regions in a graphene monolayer transmits only those quasiparticles that approach it almost perpendicularly to the n-p interface. Such a selective transmission of carriers by a single n-p junction would manifest itself in nonlocal magnetoresistance effect in arrays of such junctions and determines the unusual Fano factor in the current noise universal for the n-p junctions in graphene.

Tunable metal-insulator transition in double-layer graphene heterostructures

Disordered conductors with resistivity above the resistance quantum h/e(2) should exhibit an insulating behaviour at low temperatures, a universal phenomenon known as a strong (Anderson) localization(1-3). Observed in a multitude of materials, including damaged graphene and its disordered chemical derivatives(4-10), Anderson localization has not been seen in generic graphene, despite its resistivity near the neutrality point reaching approximate to h/e(2) per carrier type(4,5). It has remained a puzzle why graphene is such an exception. Here we report a strong localization and the corresponding metal-insulator transition in ultra-high-quality graphene. The transition is controlled externally, by changing the carrier density in another graphene layer placed at a distance of several nm and decoupled electrically. The entire behaviour is explained by electron-hole puddles that disallow localization in standard devices but can be screened out in double-layer graphene. The localization that occurs with decreasing rather than increasing disorder is a unique occurrence, and the reported double-layer heterostructures presents a new experimental system that invites further studies.

Friedel Oscillations, Impurity Scattering, and Temperature Dependence of Resistivity in Graphene

We show that Friedel oscillations (FO) in grapehene are strongly affected by the chirality of electrons in this material. In particular, the FO of the charge density around an impurity show a faster (deltarho approximately r;{-3}) decay than in conventional 2D electron systems and do not contribute to a linear temperature-dependent correction to the resistivity. In contrast, the FO of the exchange field which surrounds atomically sharp defects breaking the hexagonal symmetry of the honeycomb lattice lead to a negative linear T dependence of the resistivity.

UNIVERSALITY OF TRANSPORT PROPERTIES IN EQUILIBRIUM, THE GOLDSTONE THEOREM, AND CHIRAL ANOMALY

We study transport in a class of physical systems possessing two conserved chiral charges. We describe a relation between universality of transport properties of such systems and the chiral anomaly. We show that the nonvanishing of a current expectation v

Random resistor network model of minimal conductivity in graphene

Transport in undoped graphene is related to percolating current patterns in the networks of n- and p-type regions reflecting the strong bipolar charge density fluctuations. Finite transparency of the p-n junctions is vital in establishing the macroscopic conductivity. We propose a random resistor network model to analyze scaling dependencies of the conductance on the doping and disorder, the quantum magnetoresistance and the corresponding dephasing rate.

Spin dynamics in a one-dimensional ferromagnetic Bose Gas.

We investigate the propagation of spin excitations in a one-dimensional ferromagnetic Bose gas. While the spectrum of longitudinal spin waves in this system is soundlike, the dispersion of transverse spin excitations is quadratic, making a direct application of the Luttinger liquid theory impossible. By using a combination of different analytic methods we derive the large time asymptotic behavior of the spin-spin dynamical correlation function for strong interparticle repulsion. The result has an unusual structure associated with a crossover from the regime of trapped spin wave to an open regime and does not have analogues in known low-energy universality classes of quantum 1D systems.

Nonunitary Spin-Charge Separation in a One-Dimensional Fermion Gas

In this Letter we report exact results on the infrared asymptotics of the one-particle dynamical correlation function of the gas of impenetrable spin 1/2 fermions at infinitesimal temperature. The correlation function shows signs of spin-charge separation with scaling behavior in the charge part and exponential decay as a function of the space coordinate in the spin part. Surprisingly, the anomalous dimensions in the charge part do not correspond to any unitary conformal field theory. We find that the fermion spectral weight has a power law divergency at low energy with the anomalous exponent -1/2.

Ordered states of adatoms on graphene

We show that a dilute ensemble of epoxy-bonded adatoms on graphene has a tendency to form a spatially correlated state accompanied by a gap in graphenes electron spectrum. This effect emerges from the electron-mediated interaction between adatoms with a peculiar 1/r(3) distance dependence. The partial ordering transition is described by a random bond three-state Potts model.

Resonant dephasing in the electronic Mach-Zehnder interferometer.

We address the recently observed unexpected behavior of Aharonov-Bohm oscillations in the electronic Mach-Zehnder interferometer that was realized experimentally in a quantum Hall system [I. Neder, Phys. Rev. Lett. 96, 016804 (2006)10.1103/PhysRevLett.96.016804]. We argue that the measured lobe structure in the visibility of oscillations and the phase rigidity result from a strong long-range interaction between two adjacent counterpropagating edge states, which leads to a resonant scattering of plasmons. The visibility and phase shift, which we express in terms of the transmission coefficient for plasmons, can be used for the tomography of edge states.