900 research outputs found
Hard sphere-like dynamics in a non hard sphere liquid
The collective dynamics of liquid Gallium close to the melting point has been
studied using Inelastic X-ray Scattering to probe lengthscales smaller than the
size of the first coordination shell. %(momentum transfers, , 15
nm). Although the structural properties of this partially covalent
liquid strongly deviate from a simple hard-sphere model, the dynamics, as
reflected in the quasi-elastic scattering, are beautifully described within the
framework of the extended heat mode approximation of Enskog's kinetic theory,
analytically derived for a hard spheres system. The present work demonstrates
the applicability of Enskog's theory to non hard- sphere and non simple
liquids.Comment: 5 pages, 2 figures, accepted in Phys. Rev. Let
On the origin of the -transition in liquid Sulphur
Developing a novel experimental technique, we applied photon correlation
spectroscopy using infrared radiation in liquid Sulphur around ,
i.e. in the temperature range where an abrupt increase in viscosity by four
orders of magnitude is observed upon heating within few degrees. This allowed
us - overcoming photo-induced and absorption effects at visible wavelengths -
to reveal a chain relaxation process with characteristic time in the ms range.
These results do rehabilitate the validity of the Maxwell relation in Sulphur
from an apparent failure, allowing rationalizing the mechanical and
thermodynamic behavior of this system within a viscoelastic scenario.Comment: 5 pages, 4 eps figures, accepted in Phys. Rev. Let
Tunneling of polarized fermions in 3D double wells
We study the tunneling of a spin polarized Fermi gas in a three-dimensional
double well potential, focusing on the time dynamics starting from an initial
state in which there is an imbalance in the number of particles in the two
wells. Although fermions in different doublets of the double well tunnel with
different frequencies, we point out that (incoherent) oscillations of a large
number of particles can arise, as a consequence of the presence of transverse
degrees of freedom. Estimates of the doublet structure and of the occupation of
transverse eigenstates for a realistic experimental setup are provided.Comment: 10 pages, Typos corrected and figures changed - published in Laser
Physics, issue on the LPHYS'11 conference (Sarajevo, 2011
Quantum quench dynamics of the sine-Gordon model in some solvable limits
In connection with the the thermalization problem in isolated quantum
systems, we investigate the dynamics following a quantum quench of the
sine-Gordon model in the Luther-Emery and the semiclassical limits. We consider
the quench from the gapped to the gapless phase as well as reversed one. By
obtaining analytic expressions for the one and two-point correlation functions
of the order parameter operator at zero-temperature, the manifestations of
integrability in the absence of thermalization in the sine-Gordon model are
studied. It is thus shown that correlations in the long time regime after the
quench are well described by a generalized Gibbs ensemble. We also consider the
case where the system is initially in contact with a reservoir at finite
temperature. The possible relevance of our results to current and future
experiments with ultracold atomic systems is also critically considered.Comment: 21 pages, no figures. To appear in New J. Phys
Microscopic dynamics and relaxation processes in liquid Hydrogen Fluoride
Inelastic x-ray scattering and Brillouin light scattering measurements of the
dynamic structure factor of liquid hydrogen fluoride have been performed in the
temperature range. The data, analysed using a viscoelastic
model with a two timescale memory function, show a positive dispersion of the
sound velocity between the low frequency value and the high
frequency value . This finding confirms the existence of
a structural () relaxation directly related to the dynamical
organization of the hydrogen bonds network of the system. The activation energy
of the process has been extracted by the analysis of the temperature
behavior of the relaxation time that follows an Arrhenius law.
The obtained value for , when compared with that observed in another
hydrogen bond liquid as water, suggests that the main parameter governing the
-relaxation process is the number of the hydrogen bonds per molecule.Comment: 9 pages and 12 figure
One-dimensional fermionic systems after interaction quenches and their description by bosonic field theories
We show that the dynamics of quenches in one dimension far off equilibrium
can be described by power laws, but with exponents differing from the fully
renormalized ones at lowest energies. Instead they depend on the initial state
and its excitation energy. Furthermore, we found that for quenches to strong
interactions unexpected similarities between systems in one and in infinite
dimensions occur, indicating the dominance of local processes.Comment: This is a distinctly revised version which is focussed on the
description of the dynamics by bosonization technique
Remarks on the notion of quantum integrability
We discuss the notion of integrability in quantum mechanics. Starting from a
review of some definitions commonly used in the literature, we propose a
different set of criteria, leading to a classification of models in terms of
different integrability classes. We end by highlighting some of the expected
physical properties associated to models fulfilling the proposed criteria.Comment: 22 pages, no figures, Proceedings of Statphys 2
Zamolodchikov-Faddeev Algebra and Quantum Quenches in Integrable Field Theories
We analyze quantum quenches in integrable models and in particular the
determination of the initial state in the basis of eigenstates of the
post-quench hamiltonian. This leads us to consider the set of transformations
of creation and annihilation operators that respect the Zamolodchikov-Faddeev
algebra satisfied by integrable models. We establish that the Bogoliubov
transformations hold only in the case of quantum quenches in free theories. In
the most general case of interacting theories, we identify two classes of
transformations. The first class induces a change in the S-matrix of the theory
but not of its ground state, whereas the second class results in a "dressing"
of the operators. As examples of our approach we consider the transformations
associated with a change of the interaction in the Sinh-Gordon and the
Lieb-Liniger model.Comment: v2: published version (typos corrected
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