628 research outputs found
Topological quantum transition driven by charge-phonon coupling in the Haldane Chern insulator
In condensed matter physics many features can be understood in terms of their
topological properties. Here we report evidence of a topological quantum
transition driven by the charge-phonon coupling in the spinless Haldane model
on a honeycomb lattice, a well-known prototypical model of Chern insulator.
Starting from parameters describing the topological phase in the bare Haldane
model, we show that the increasing of the strength of the charge lattice
coupling drives the system towards a trivial insulator. The average number of
fermions in the Dirac point, characterized by the lowest gap, exhibits a finite
discontinuity at the transition point and can be used as direct indicator of
the topological quantum transition. Numerical simulations show, also, that the
renormalized phonon propagator exhibits a two peak structure across the quantum
transition, whereas, in absence of the mass term in the bare Hadane model,
there is indication of a complete softening of the effective vibrational mode
signaling a charge density wave instability.Comment: 5 pages, 4 figure
Possible Micrometeorological Anomalies Induced by Volcanic Activity Recorded at Stromboli Island (Aeolian Archipelago, Italy)
Hourly values of atmospheric pressure and air temperature have been acquired at the top of two volcanic islands, Stromboli and
Salina in the Aeolian Archipelago (Italy), very similar in height and morphology but completely different with regard to their
volcanic activity state: the former is permanently active, whereas the latter is extinguished. During the last four years Stromboli
experienced normal activity, volcanic unrests, and an effusive eruption (AugustâNovember 2014).The comparative analysis of the
recorded data, both in the time and frequency domains, evidenced a peculiar micrometeorological regime at Stromboli, more
turbulent during unrests with respect to the quieter periods, but showing an apparent paradox during eruptions, characterized
by a lower atmospheric turbulence. These observations suggest that the studied volcanic-micrometeorological system is chaotic,
due to contemporary opposite transients generated in the atmosphere by volcanic activity changes, and that micrometeorological
conditions in volcanic areas are controlled both by exogenous processes and volcanic activity
Non Abelian BF theories with sources and 2-D gravity
We study the interaction of non-Abelian topological theories defined on
two dimensional manifolds with point sources carrying non-Abelian charges. We
identify the most general solution for the field equations on simply and
multiply connected two-manifolds. Taking the particular choice of the so-called
extended Poincar\'e group as the gauge group we discuss how recent discussions
of two dimensional gravity models do fit in this formalism.Comment: 20 pages, Latex, To appear in Phys Rev D5
Two channel model for optical conductivity of high mobility organic crystals
We show that the temperature dependence of conductivity of high mobility
organic crystals Pentacene and Rubrene can be quantitatively described in the
framework of the model where carriers are scattered by quenched local
impurities and interact with phonons by Su-Schrieffer-Hegger (SSH) coupling.
Within this model, we present approximation free results for mobility and
optical conductivity obtained by world line Monte Carlo, which we generalize to
the case of coupling both to phonons and impurities. We find fingerprints of
carrier dynamics in these compounds which differ from conventional metals and
show that the dynamics of carriers can be described as a superposition of a
Drude term representing diffusive mobile particles and a Lorentz term
associated with dynamics of localized charges.Comment: 6 pages, 5 figure
Gauge Formulation of the Spinning Black Hole in (2+1)-Dimensional Anti-de Sitter Space
We compute the group element of SO(2,2) associated with the spinning black
hole found by Ba\~nados, Teitelboim and Zanelli in (2+1)-dimensional anti-de
Sitter space-time. We show that their metric is built with SO(2,2) gauge
invariant quantities and satisfies Einstein's equations with negative
cosmological constant everywhere except at . Moreover, although the metric
is singular on the horizons, the group element is continuous and possesses a
kink there.Comment: 10 page
Geomorphological and geochemical characterization of the 11 August 2008 mud volcano eruption at S. Barbara village (Sicily, Italy) and its possible relationship with seismic activity
On 11 August 2008 a paroxysmal eruption occurred at Santa Barbara mud volcano (MV), located close to Caltanissetta, one of the most densely populated cities of Sicily (Italy). An associated minor event took place on August 2009. Both the events caused severe damage to civil infrastructures located within a range of about 2 km from the eruptive vent. Geomorphological, geochemical, and seismological investigations were carried out for framing the events in the appropriate geodynamic context. Geomorphological surveys recognized, in the immediate surrounding of the main emission point, two different families of processes and landforms: (i) ground deformations and (ii) changes in morphology and number of the fluid emitting vents. These processes were associated to a wider network of fractures, seemingly generated by the shock wave produced by the gas blast that occurred at the main paroxysm. Geochemical characterization allowed an estimation of the source of the fluids, or at least their last standing, at about 3 km depth. Finally, the close time relationships observed between anomalous increments of seismic activity and the two main paroxysmal events accounted for a possible common trigger for both the phenomena, even with different timing due to the very different initial conditions and characteristics of the two processes, i.e. seismogenesis and gas overloading
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