246 research outputs found
Superconductivity in a two dimensional extended Hubbard model
The Roth's two-pole approximation has been used by the present authors to
investigate the role of hybridization in the superconducting properties
of an extended Hubbard model. Superconductivity with singlet
-wave pairing is treated by following Beenen and Edwards
formalism. In this work, the Coulomb interaction, the temperature and the
superconductivity have been considered in the calculation of some relevant
correlation functions present in the Roth's band shift. The behavior of the
order parameter associated with temperature, hybridization, Coulomb interaction
and the Roth's band shift effects on superconductivity are studied.Comment: 14 pages, 8 figures, accepted for publication in European Physical
Journal
Specific heat of a non-local attractive Hubbard model
The specific heat of an attractive (interaction ) non-local Hubbard
model is investigated. We use a two-pole approximation which leads to a set of
correlation functions. In particular, the correlation function $\
G\delta\delta=1-n_Tn_T=n_{\uparrow}+n_{\downarrow}(0,\pm\pi)(\pm\pi,0)$ eliminates the two peak structure, the low
temperature peak remaining. The effects of the second nearest neighbor hopping
on the specific heat are also investigated.Comment: 5 pages, 7 figure
Magnetic transitions induced by pressure and magnetic field in a two-orbital -electron model in cubic and tetragonal lattices
We investigate the onset and evolution of under the simultaneous application
of pressure and magnetic field of distinct itinerant N\'eel states using the
underscreened Anderson Lattice Model (UALM) which has been proposed to describe
-electron systems. The model is composed by two narrow -bands (of either
or character) that hybridize with a wide -band and local
-electron interactions. We consider both cubic and tetragonal lattices. The
N\'eel order parameters and are assumed to be
fixed by an Ising anisotropy. The applied magnetic field is parallel to
the anisotropy axis. It has been assumed that the variation of the band width
is sensitive to pressure. In the absence of a magnetic field, the increase
of takes the system from the phase AF to another phase AF. The
phase AF occurs when while in the AF
phase the gaps satisfy . In the presence of a
magnetic field , the phase AF is quickly suppressed and reappears
again at intermediate values of the magnetic field while it is predominant at
higher magnetic fields. The analysis of the partial density of states close to
the phase transition between the phases AF and AF, allows a better
understanding the mechanism responsible whereby the transition is induced by an
increase in the magnetic field. As a important general result, we found that
the magnetic field favours the phase AF while the phase AF is
suppressed. For the tetragonal lattice, the phase AF is even more favored
when and increases concomitantly, where and are the lattice
parameters
Attosecond spectroscopy of bio-chemically relevant molecules
Understanding the role of the electron dynamics in the photochemistry of bio-chemically relevant molecules is key to getting access to the fundamental physical processes leading to damage, mutation and, more generally, to the alteration of the final biological functions. Sudden ionization of a large molecule has been proven to activate a sub-femtosecond charge flow throughout the molecular backbone, purely guided by electronic coherences, which could ultimately affect the photochemical response of the molecule at later times. We can follow this ultrafast charge flow in real time by exploiting the extreme time resolution provided by attosecond light sources. In this work recent advances in attosecond molecular physics are presented with particular focus on the investigation of bio-relevant molecules
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