15,326 research outputs found
Microscopic theory of network glasses
A molecular theory of the glass transition of network forming liquids is
developed using a combination of self-consistent phonon and liquid state
approaches. Both the dynamical transition and the entropy crisis characteristic
of random first order transitions are mapped out as a function of the degree of
bonding and the density. Using a scaling relation for a soft-core model to
crudely translate the densities into temperatures, the theory predicts that the
ratio of the dynamical transition temperature to the laboratory transition
temperature rises as the degree of bonding increases, while the Kauzmann
temperature falls relative to the laboratory transition. These results indicate
why highly coordinated liquids should be "strong" while van der Waals liquids
without coordination are "fragile".Comment: slightly revised version that has been accepted for publication in
Phys. Rev. Let
The microscopic theory of fission
Fission-fragment properties have been calculated for thermal neutron-induced
fission on a target, using constrained
Hartree-Fock-Bogoliubov calculations with a finite-range effective interaction.
A quantitative criterion based on the interaction energy between the nascent
fragments is introduced to define the scission configurations. The validity of
this criterion is benchmarked against experimental measurements of the kinetic
energies and of multiplicities of neutrons emitted by the fragments.Comment: 8 page, 4 figures, to be published in Proceedings of the 4th
International Workshop on Fission and Fission Product Spectroscop
Effective Vortex Mass from Microscopic Theory
We calculate the effective mass of a single quantized vortex in the BCS
superconductor at finite temperature. Based on effective action approach, we
arrive at the effective mass of a vortex as integral of the spectral function
divided by over frequency. The spectral function is
given in terms of the quantum-mechanical transition elements of the gradient of
the Hamiltonian between two Bogoliubov-deGennes (BdG) eigenstates. Based on
self-consistent numerical diagonalization of the BdG equation we find that the
effective mass per unit length of vortex at zero temperature is of order (=Fermi momentum, =coherence length), essentially
equaling the electron mass displaced within the coherence length from the
vortex core. Transitions between the core states are responsible for most of
the mass. The mass reaches a maximum value at and decreases
continuously to zero at .Comment: Supercedes prior version, cond-mat/990312
Microscopic Theory of Josephson Mesoscopic Constrictions
We present a microscopic theory for the d.c. Josephson effect in model
mesoscopic constrictions. Our method is based on a non-equilibrium Green
function formalism which allows for a self-consistent determination of the
order parameter profile along the constriction. The various regimes defined by
the different length scales (Fermi wavelength , coherence length
and constriction length ) can be analyzed, including the case
where all these lengths are comparable. For the case phase oscillations with spatial period can be
observed. In the case of solutions with a phase-slip center inside
the constriction can be found, in agreement with previous phenomenological
theories.Comment: 4 pages (RevTex 3.0), 3 postscript figures available upon request,
312456-C
Microscopic theory of the Andreev gap
We present a microscopic theory of the Andreev gap, i.e. the phenomenon that
the density of states (DoS) of normal chaotic cavities attached to
superconductors displays a hard gap centered around the Fermi energy. Our
approach is based on a solution of the quantum Eilenberger equation in the
regime , where and are the classical dwell time and
Ehrenfest-time, respectively. We show how quantum fluctuations eradicate the
DoS at low energies and compute the profile of the gap to leading order in the
parameter .Comment: 4 pages, 3 figures; revised version, more details, extra figure, new
titl
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