Magnetic spectrum of trigonally warped bilayer graphene - semiclassical analysis, zero modes, and topological winding numbers

We investigate the fine structure in the energy spectrum of bilayer graphene in the presence of various stacking defaults, such as a translational or rotational mismatch. This fine structure consists of four Dirac points that move away from their original positions as a consequence of the mismatch and eventually merge in various manners. The different types of merging are described in terms of topological invariants (winding numbers) that determine the Landau-level spectrum in the presence of a magnetic field as well as the degeneracy of the levels. The Landau-level spectrum is, within a wide parameter range, well described by a semiclassical treatment that makes use of topological winding numbers. However, the latter need to be redefined at zero energy in the high-magnetic-field limit as well as in the vicinity of saddle points in the zero-field dispersion relation.Comment: 17 pages, 16 figures; published version with enhanced discussion of experimental finding

Quantum Hall effects of graphene with multi orbitals: Topological numbers, Boltzmann conductance and Semi-classical quantization

Hall conductance $\sigma_{xy}$ as the Chern numbers of the Berry connection in the magnetic Brillouin zone is calculated for a realistic multi band tight-band model of graphene with non-orthogonal basis. It is confirmed that the envelope of $\sigma_{xy}$ coincides with a semi-classical result when magnetic field is sufficiently small. The Hall resistivity $\rho_{xy}$ from the weak-field Boltzmann theory also explains the overall behaviour of the $\sigma_{xy}$ if the Fermi surface is composed of a single energy band. The plateaux of $\sigma_{xy}$ are explained from semi-classical quantization and necessary modification is proposed for the Dirac fermion regimes.Comment: 5pages, 3figure

Bose-Einstein Condensates in Strongly Disordered Traps

A Bose-Einstein condensate in an external potential consisting of a superposition of a harmonic and a random potential is considered theoretically. From a semi-quantitative analysis we find the size, shape and excitation energy as a function of the disorder strength. For positive scattering length and sufficiently strong disorder the condensate decays into fragments each of the size of the Larkin length ${\cal L}$. This state is stable over a large range of particle numbers. The frequency of the breathing mode scales as $1/{\cal L}^2$. For negative scattering length a condensate of size ${\cal L}$ may exist as a metastable state. These finding are generalized to anisotropic traps

Magnetic double refraction in piezoelectrics

A new type of magneto-optical effect in piezoelectrics is predicted. A low frequency behavior of Faraday effect is found.Comment: 2 pages, to be published in Europhys. Lett

Electron energy spectrum and the Berry phase in graphite bilayer

We emphasize that there exist four Dirac-type points in the electron-energy spectrum of a graphite bilayer near the point K of its Brillouin zone. One of the Dirac points is at the point K, and three Dirac points lie nearby. Each of these three points generates the Berry phase $\pi$, while the Dirac point at K gives the phase $-\pi$. It is these four points that determine the Berry phase in the bilayer. If an electron orbit surrounds all these points, the Berry phase is equal to $2\pi$.Comment: 4 pages, 2 figures, submitted to Phys. Rev. B ; expande

Defect-Induced Resonant Tunneling of Electromagnetic Waves Through a Polariton Gap

We consider tunneling of electromagnetic waves through a polariton band gap of a 1-D chain of atoms. We analytically demonstrate that a defect embedded in the structure gives rise to the resonance transmission at the frequency of a local polariton state associated with the defect.Comment: 5 pages, RevTe

Thermoelectric power of Ba(Fe1-xRux)2As2 and Ba(Fe1-xCox)2As2: possible changes of Fermi surface with and without changes in electron count

Temperature-dependent, in-plane, thermoelectric power (TEP) data are presented for Ba(Fe1-xRux)2As2 (0 < x < 0.36) single crystals. The previously outlined x - T phase diagram for this system is confirmed. The analysis of TEP evolution with Ru-doping suggests significant changes in the electronic structure, correlations and/or scattering occurring near ~7% and ~30% of Ru-doping levels. These results are compared with an extended set of TEP data for the electron-doped Ba(Fe1-xCox)2As2 series

Far-from-equilibrium Ostwald ripening in electrostatically driven granular powders

We report the first experimental study of cluster size distributions in electrostatically driven granular submonolayers. The cluster size distribution in this far-from-equilibrium process exhibits dynamic scaling behavior characteristic of the (nearly equilibrium) Ostwald ripening, controlled by the attachment and detachment of the "gas" particles. The scaled size distribution, however, is different from the classical Wagner distribution obtained in the limit of a vanishingly small area fraction of the clusters. A much better agreement is found with the theory of Conti et al. [Phys. Rev. E 65, 046117 (2002)] which accounts for the cluster merger.Comment: 5 pages, to appear in PR

Acoustic Spectroscopy of the DNA in GHz range

We find a parametric resonance in the GHz range of the DNA dynamics, generated by pumping hypersound . There are localized phonon modes caused by the random structure of elastic modulii due to the sequence of base pairs

Density of states in an optical speckle potential

We study the single particle density of states of a one-dimensional speckle potential, which is correlated and non-Gaussian. We consider both the repulsive and the attractive cases. The system is controlled by a single dimensionless parameter determined by the mass of the particle, the correlation length and the average intensity of the field. Depending on the value of this parameter, the system exhibits different regimes, characterized by the localization properties of the eigenfunctions. We calculate the corresponding density of states using the statistical properties of the speckle potential. We find good agreement with the results of numerical simulations.Comment: 11 pages, 11 figures, revtex