Theory of magnetic oscillations in Weyl semimetals

Weyl semimetals are a new class of Dirac material that posses bulk energy nodes in three dimensions. In this paper, we study a Weyl semimetal subject to an applied magnetic field. We derive expressions for the density of states, electronic specific heat, and the quantum oscillations of the magnetization, DC conductivity, and thermal conductivity. We find phase shifts in the quantum oscillations that distinguish the Weyl semimetal from conventional three dimensional Schr\"odinger Fermions.Comment: 11 pages, 5 figure

Impact of Electron-Phonon Coupling on Near-Field Optical Spectra

The finite momentum transfer ($\boldsymbol{q}$) longitudinal optical response $\sigma^L(\boldsymbol{q},\omega)$ of graphene has a peak at an energy $\omega=\hbar v_F q$. This corresponds directly to a quasiparticle peak in the spectral density at momentum relative to the Fermi momentum $k_F -q$. Inclusion of coupling to a phonon mode at $\omega_E$ results, for $\omega<|\omega_E|$, in a constant electron-phonon renormalization of the bare bands by a mass enhancement factor $(1+\lambda)$ and this is followed by a phonon kink at $\omega_E$ where additional broadening begins. Here we study the corresponding changes in the optical quasiparticle peaks which we find to continue to directly track the renormalized quasiparticle energies until $q$ is large enough that the optical transitions begin to sample the phonon kink region of the dispersion curves where linearity in momentum is lost in the renormalized Dirac Fermion dispersion curves and the correspondence to a single quasiparticle energy is lost. Nevertheless there remains in $\sigma^L(\boldsymbol{q},\omega)$ features analogous to the phonon kinks of the dispersion curves which are observable through variation of $q$ and $\omega$.Comment: 6 pages, 5 figure

Suppression of Spontaneous Supercurrents in a Chiral p-Wave Superconductor

The superconducting state of SRO is widely believed to have chiral p-wave order that breaks time reversal symmetry. Such a state is expected to have a spontaneous magnetization, both at sample edges and at domain walls between regions of different chirality. Indeed, muon spin resonance experiments are interpreted as evidence of spontaneous magnetization due to domain walls or defects in the bulk. However, recent magnetic microscopy experiments place upper limits on the magentic fields at the sample edge and surface which are as much as two orders of magnitude smaller than the fields predicted theoretically for a somewhat idealized chiral p-wave superconductor. We investigate the effects on the spontaneous supercurrents and magnetization of rough and pair breaking surfaces for a range of parameters within a Ginzburg-Landau formalism. The effects of competing orders nucleated at the surface are also considered. We find the conditions under which the edge currents are significantly reduced while leaving the bulk domain wall currents intact, are quite limited. The implications for interpreting the existing body of experimental results on superconducting SRO within a chiral p-wave model are discussed.Comment: Changes to section 3, typos remove

Reclaiming human machine nature

Extending and modifying his domain of life by artifact production is one of the main characteristics of humankind. From the first hominid, who used a wood stick or a stone for extending his upper limbs and augmenting his gesture strength, to current systems engineers who used technologies for augmenting human cognition, perception and action, extending human body capabilities remains a big issue. From more than fifty years cybernetics, computer and cognitive sciences have imposed only one reductionist model of human machine systems: cognitive systems. Inspired by philosophy, behaviorist psychology and the information treatment metaphor, the cognitive system paradigm requires a function view and a functional analysis in human systems design process. According that design approach, human have been reduced to his metaphysical and functional properties in a new dualism. Human body requirements have been left to physical ergonomics or "physiology". With multidisciplinary convergence, the issues of "human-machine" systems and "human artifacts" evolve. The loss of biological and social boundaries between human organisms and interactive and informational physical artifact questions the current engineering methods and ergonomic design of cognitive systems. New developpment of human machine systems for intensive care, human space activities or bio-engineering sytems requires grounding human systems design on a renewed epistemological framework for future human systems model and evidence based "bio-engineering". In that context, reclaiming human factors, augmented human and human machine nature is a necessityComment: Published in HCI International 2014, Heraklion : Greece (2014

Boundary-layer transition and displacement thickness effects on zero-lift drag of a series of power-law bodies at Mach 6

Wave and skin-friction drag have been numerically calculated for a series of power-law bodies at a Mach number of 6 and Reynolds numbers, based on body length, from 1.5 million to 9.5 million. Pressure distributions were computed on the nose by the inverse method and on the body by the method of characteristics. These pressure distributions and the measured locations of boundary-layer transition were used in a nonsimilar-boundary-layer program to determine viscous effects. A coupled iterative approach between the boundary-layer and pressure-distribution programs was used to account for boundary-layer displacement-thickness effects. The calculated-drag coefficients compared well with previously obtained experimental data

The Active Nucleus of IC4970: A Nearby Example of Merger-Induced Cold-Gas Accretion

We present results from Chandra X-ray and Spitzer mid-infrared observations of the interacting galaxy pair NGC6872/IC4970 in the Pavo galaxy group and show that the smaller companion galaxy IC4970 hosts a highly obscured active galactic nucleus (AGN). The 0.5-10 keV X-ray luminosity of the nucleus is variable, increasing by a factor 2.9 to 1.7 x 10^{42} erg/s (bright state) on ~100 ks timescales. The X-ray spectrum of the is heavily absorbed (N_H = 3 x 10^{23} cm^{-2}) for power law models with Gamma = 1.5-2.0 and shows a clear 6.4 keV Fe Kalpha line with equivalent width of 144-195 eV. Limits on the diffuse emission in IC4970 from Chandra X-ray data suggest that the available power from Bondi accretion of hot interstellar gas may be an order of magnitude too small to power the AGN. Spitzer images show that 8 micron nonstellar emission is concentrated in the central 1 kpc of IC4970, consistent with high obscuration in this region. The mid-infrared colors of the nucleus are consistent with those expected for a highly obscured AGN. Taken together these data suggest that the nucleus of IC4970 is a Seyfert 2, triggered and fueled by cold material supplied to the central supermassive black hole as a result of the off-axis collision of IC4970 with the cold-gas rich spiral galaxy NGC6872.Comment: 10 pages, 9 figures, submitted to ApJ, MIR flux conversion error corrected in Table 4, MIR colors and paper text unchange

Extended Fermi coordinates

We extend the notion of Fermi coordinates to a generalized definition in which the highest orders are described by arbitrary functions. From this definition rises a formalism that naturally gives coordinate transformation formulae. Some examples are developped in which the extended Fermi coordinates simplify the metric components.Comment: 16 pages, 1 figur