Quasiparticle scattering and local density of states in graphite

We determine the effect of quasiparticle interference on the spatial variations of the local density of states (LDOS) in graphite in the neighborhood of an isolated impurity. A number of characteristic behaviors of interference are identified in the Fourier transformed spectrum. A comparison between our results and scanning tunneling microscopy (STM) experiments could provide a critical test of the range (of energy) of applicability of the Fermi liquid description of graphite, where some evidence of the breakdown of Fermi liquid theory has recently been discussed. Moreover, given the similarity between the band structures of graphite and that of nodal quasiparticles in a d-wave superconductor, a comparison between results in the two materials is useful for understanding the physics of the cuprates.Comment: 5 pages, 4 figures, RevTex

Emergent Higgsless Superconductivity

We present a new Higgsless model of superconductivity, inspired from anyon superconductivity but P- and T-invariant and generalizable to any dimension. While the original anyon superconductivity mechanism was based on incompressible quantum Hall fluids as average field states, our mechanism involves topological insulators as average field states. In D space dimensions it involves a (D-1)-form fictitious pseudovector gauge field which originates from the condensation of topological defects in compact low-energy effective BF theories. There is no massive Higgs scalar as there is no local order parameter. When electromagnetism is switched on, the photon acquires mass by the topological BF mechanism. Although the charge of the gapless mode (2) and the topological order (4) are the same as those of the standard Higgs model, the two models of superconductivity are clearly different since the origins of the gap, reflected in the high-energy sectors are totally different. In 2D this type of superconductivity is explicitly realized as global superconductivity in Josephson junction arrays. In 3D this model predicts a possible phase transition from topological insulators to Higgsless superconductors.Comment: Prepared for the proceedings of the XII Quark Confinement and the Hadron Spectrum, 29 August to 3 September 2016, Thessaloniki, Greece. arXiv admin note: substantial text overlap with arXiv:1408.506

Strongly and Weakly Unstable Anisotropic Quark-Gluon Plasma

Using explicit solutions of the QCD transport equations, we construct an effective potential for an anisotropic quark-gluon plasma which under plausible assumptions holds beyond the Hard Loop approximation. The configurations, which are unstable in the linear response approach, are characterized by a negative quadratic term of the effective potential. The signs of higher order terms can be either negative or positive, depending on the parton momentum distribution. In the case of a Gaussian momentum distribution, the potential is negative and unbound from below. Therefore, the modes, which are unstable for gauge fields of small amplitude, remain unstable for arbitrary large amplitudes. We also present an example of a momentum distribution which gives a negative quadratic term of the effective potential but the whole potential has a minimum and it grows for sufficiently large gauge fields. Then, the system is weakly unstable. The character of the instability is important for the dynamical evolution of the plasma system.Comment: 13 pages, 1 figure, revised, to appear in Phys. Rev.

Riots, coups and civil war : revisiting the greed and grievance debate

The most influential recent work on the determinants of civil wars found the factors associated with the grievance motivation to be largely irrelevant. Our paper subjects the results of this empirical work to further scrutiny by embedding the study of civil war in a more general analysis of varieties of violent contestation of political power within the borders of the state. Such an approach, we argue, will have important implications for how we think theoretically about the occurrence of domestic war as well as how we specify our empirical tests. In the empirical model, the manifestation of domestic conflict range from low intensity violence and coups to civil war. Our multinomial specification of domestic conflict supports the hypothesis that diversity accentuates distributional conflict and thus increases the risk of civil war. We also find that democracies may be more efficient than autocracies in reducing the risk of civil war.Post Conflict Reconstruction,Population Policies,Social Conflict and Violence,Peace&Peacekeeping,Hazard Risk Management

The tunneling conductance between a superconducting STM tip and an out-of-equilibrium carbon nanotube

We calculate the current and differential conductance for the junction between a superconducting (SC) STM tip and a Luttinger liquid (LL). For an infinite single-channel LL, the SC coherence peaks are preserved in the tunneling conductance for interactions weaker than a critical value, while for strong interactions (g <0.38), they disappear and are replaced by cusp-like features. For a finite-size wire in contact with non-interacting leads, we find however that the peaks are restored even for extremely strong interactions. In the presence of a source-drain voltage the peaks/cusps split, and the split is equal to the voltage. At zero temperature, even very strong interactions do not smear the two peaks into a broader one; this implies that the recent experiments of Y.-F. Chen et. al. (Phys. Rev. Lett. 102, 036804 (2009)) do not rule out the existence of strong interactions in carbon nanotubes.Comment: 8 pages, 3 figure

From topological insulators to superconductors and Confinement

Topological matter in 3D is characterized by the presence of a topological BF term in its long-distance effective action. We show that, in 3D, there is another marginal term that must be added to the action in order to fully determine the physical content of the model. The quantum phase structure is governed by three parameters that drive the condensation of topological defects: the BF coupling, the electric permittivity and the magnetic permeability of the material. For intermediate levels of electric permittivity and magnetic permeability the material is a topological insulator. We predict, however, new states of matter when these parameters cross critical values: a topological superconductor when electric permittivity is increased and magnetic permeability is lowered and a charge confinement phase in the opposite case of low electric permittivity and high magnetic permeability. Synthetic topological matter may be fabricated as 3D arrays of Josephson junctions.Comment: 5 pages, no figures, few references added, typos corrected and few comments adde

Extreme intensity pulses in a semiconductor laser with a short external cavity

We present a numerical study of the pulses displayed by a semiconductor laser with optical feedback in the short cavity regime, such that the external cavity round trip time is smaller than the laser relaxation oscillation period. For certain parameters there are occasional pulses, which are high enough to be considered extreme events. We characterize the bifurcation scenario that gives rise to such extreme pulses and study the influence of noise. We demonstrate intermittency when the extreme pulses appear and hysteresis when the attractor that sustains these pulses is destroyed. We also show that this scenario is robust under the inclusion of noise