2,292 research outputs found
Phonon Squeezing in a Superconducting Molecular Transistor
Josephson transport through a single molecule or carbon nanotube is
considered in the presence of a local vibrational mode coupled to the
electronic charge. The ground-state solution is obtained exactly in the limit
of a large superconducting gap, and is extended to the general case by
variational analysis. Coherent charge fluctuations are entangled with
non-classical phonon states. The Josephson current induces squeezing of the
phonon mode, which is controlled by the superconducting phase difference and by
the junction asymmetry. Optical probes of non-classical phonon states are
briefly discussed
Ground state overlap and quantum phase transitions
We present a characterization of quantum phase transitions in terms of the
the overlap function between two ground states obtained for two different
values of external parameters. On the examples of the Dicke and XY models, we
show that the regions of criticality of a system are marked by the extremal
points of the overlap and functions closely related to it. Further, we discuss
the connections between this approach and the Anderson orthogonality
catastrophe as well as with the dynamical study of the Loschmidt echo for
critical systems.Comment: 5 pages. Version to be published, title change
Polaron self-trapping in a honeycomb net
Small polaron behavior in a two dimensional honeycomb net is studied by
applying the strong coupling perturbative method to the Holstein molecular
crystal model. We find that small optical polarons can be mobile also if the
electrons are strongly coupled to the lattice. Before the polarons localize and
become very heavy, there is infact a window of {\it e-ph} couplings in which
the polarons are small and have masses of order times the bare
band mass according to the value of the adiabaticity parameter. The 2D
honeycomb net favors the mobility of small optical polarons in comparison with
the square lattice.Comment: 6 pages, 3 figures, to appear in J.Phys.:Condensed Matter {PACS:
63.10.+a, 63.20.Dj, 71.38.+i
Model Calculation of Electron-Phonon Couplings in a Dimer with a Non-Degenerate Orbital
We evaluate all the electron-phonon couplings derived from the one-body
electronic interactions, in both the adiabatic and extreme non-adiabatic limit,
for a dimer with a non-degenerate orbital built from atomic wave functions of
Gaussian shape. We find largely different values of the coupling parameters in
the two cases, as well as different expressions of the corresponding terms in
the Hamiltonian.Comment: 5 postscript figure
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