770 research outputs found
Momentum-resolved electron-phonon interaction in lead determined by neutron resonance spin-echo spectroscopy
Neutron resonance spin-echo spectroscopy was used to monitor the temperature
evolution of the linewidths of transverse acoustic phonons in lead across the
superconducting transition temperature, , over an extended range of the
Brillouin zone. For phonons with energies below the superconducting energy gap,
a linewidth reduction of maximum amplitude eV was observed below
. The electron-phonon contribution to the phonon lifetime extracted from
these data is in satisfactory overall agreement with {\it ab-initio}
lattice-dynamical calculations, but significant deviations are found
Mass loss and longevity of gravitationally bound oscillating scalar lumps (oscillatons) in D-dimensions
Spherically symmetric oscillatons (also referred to as oscillating soliton
stars) i.e. gravitationally bound oscillating scalar lumps are considered in
theories containing a massive self-interacting real scalar field coupled to
Einstein's gravity in 1+D dimensional spacetimes. Oscillations are known to
decay by emitting scalar radiation with a characteristic time scale which is,
however, extremely long, it can be comparable even to the lifetime of our
universe. In the limit when the central density (or amplitude) of the
oscillaton tends to zero (small-amplitude limit) a method is introduced to
compute the transcendentally small amplitude of the outgoing waves. The results
are illustrated in detail on the simplest case, a single massive free scalar
field coupled to gravity.Comment: 23 pages, 2 figures, references on oscillons added, version to appear
in Phys. Rev.
Non exponential relaxation in fully frustrated models
We study the dynamical properties of the fully frustrated Ising model. Due to
the absence of disorder the model, contrary to spin glass, does not exhibit any
Griffiths phase, which has been associated to non-exponential relaxation
dynamics. Nevertheless we find numerically that the model exhibits a stretched
exponential behavior below a temperature T_p corresponding to the percolation
transition of the Kasteleyn-Fortuin clusters. We have also found that the
critical behavior of this clusters for a fully frustrated q-state spin model at
the percolation threshold is strongly affected by frustration. In fact while in
absence of frustration the q=1 limit gives random percolation, in presence of
frustration the critical behavior is in the same universality class of the
ferromagnetic q=1/2-state Potts model.Comment: 7 pages, RevTeX, 11 figs, to appear on Physical Review
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