Showing papers by "Irina V. Grigorieva published in 2005"

Two-dimensional gas of massless Dirac fermions in graphene

Abstract: Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrodinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.

Tilt of pancake vortex stacks in layered superconductors in the crossing lattice regime

Abstract: We study crossing vortices in strongly anisotropic Bi2Sr2CaCu2O8+delta single crystals Using scanning Hall probe microscopy and Bitter decoration techniques, we find an asymmetry of magnetic field profiles produced by pancake vortices (PVs), which are interacting with Josephson vortices (JVs), near the surface of the crystal We attribute the observed asymmetry to a substantial tilt (14-18 degrees) of PV stacks, which is produced by the torque due to the surface currents and JVs We calculate the tilt angle and obtain agreement with experimental data when the irreversible in-plane magnetization is included A further refinement to the model is considered which accounts for a reduction in the PV stack line tension near the sample surface

Nonlocal Response and Surface-Barrier-Induced Rectification in Hall-Shaped Mesoscopic Superconductors

Abstract: Nonlocal response in Hall-shaped superconductors is studied using the time-dependent Ginzburg-Landau equations. Applying current in one pair of contacts leads to a voltage drop in another pair of contacts situated at a distance much larger than the coherence length. This effect is a consequence of the long range correlations in a one-dimensional vortex lattice squeezed in a narrow channel by screening currents. The discrete change in the number of vortices in the channel with applied magnetic field leads to a nonlocal response which is a nonmonotonous function of the magnetic field. For specific configurations of the Hall-shaped superconductor we found a rectifying effect.

Intrinsic Pinning of a Ferromagnetic Domain Wall in Yttrium Iron Garnet Films with Strong Uniaxial Anisotropy

Abstract: Movements of individual domain walls in a ferromagnetic garnet were studied with angstrom resolution. The measurements reveal that domain walls can be locked between adjacent crystallographic planes and propagate by distinct steps matching the lattice periodicity.

Ferromagnetic domain wall on nanometer scale

Abstract: Movements of individual domain walls in a ferromagnetic garnet were studied with angstrom resolution. The measurements reveal that domain walls can be locked between adjacent crystallographic planes and propagate by distinct steps matching the lattice periodicity.