6 research outputs found
Stability of junction configurations in ferromagnet-superconductor heterostructures
We investigate the stability of possible order parameter configurations in
clean layered heterostructures of the type, where is a
superconductor and a ferromagnet. We find that for most reasonable values
of the geometric parameters (layer thicknesses and number) and of the material
parameters (such as magnetic polarization, wavevector mismatch, and oxide
barrier strength) several solutions of the {\it self consistent} microscopic
equations can coexist, which differ in the arrangement of the sequence of ``0''
and ``'' junction types (that is, with either same or opposite sign of the
pair potential in adjacent layers). The number of such coexisting self
consistent solutions increases with the number of layers. Studying the relative
stability of these configurations requires an accurate computation of the small
difference in the condensation free energies of these inhomogeneous systems. We
perform these calculations, starting with numerical self consistent solutions
of the Bogoliubov-de Gennes equations. We present extensive results for the
condensation free energies of the different possible configurations, obtained
by using efficient and accurate numerical methods, and discuss their relative
stabilities. Results for the experimentally measurable density of states are
also given for different configurations and clear differences in the spectra
are revealed. Comprehensive and systematic results as a function of the
relevant parameters for systems consisting of three and seven layers (one or
three junctions) are given, and the generalization to larger number of layers
is discussed.Comment: 17 pages, including 14 Figures. Higher resolution figures available
from the author
Dyson's Brownian Motion and Universal Dynamics of Quantum Systems
We establish a correspondence between the evolution of the distribution of
eigenvalues of a matrix subject to a random Gaussian perturbing
matrix, and a Fokker-Planck equation postulated by Dyson. Within this model, we
prove the equivalence conjectured by Altshuler et al between the space-time
correlations of the Sutherland-Calogero-Moser system in the thermodynamic limit
and a set of two-variable correlations for disordered quantum systems
calculated by them. Multiple variable correlation functions are, however, shown
to be inequivalent for the two cases.Comment: 10 pages, revte
Composite Fermion Description of Correlated Electrons in Quantum Dots: Low Zeeman Energy Limit
We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}Comment: 15 pages, 7 postscript figure
Apparent viscosity and particle pressure of a concentrated suspension of non-Brownian hard spheres near the jamming transition
We consider the steady shear flow of a homogeneous and dense assembly of hard spheres suspended in a Newtonian viscous fluid. In a first part, a mean-field approach based on geometric arguments is used to determine the viscous dissipation in a dense isotropic suspension of smooth hard spheres and the hydrodynamic contribution to the suspension viscosity. In a second part, we consider the coexistence of transient solid clusters coupled to regions with free flowing particles near the jamming transition. The fraction of particles in transient clusters is derived through the Landau-Ginzburg concepts for first-order phase transition with an order parameter corresponding to the proportion of “solid” contacts. A state equation for the fraction of particle-accessible volume is introduced to derive the average normal stresses and a constitutive law that relates the total shear stress to the shear rate. The analytical expression of the average normal stresses well accounts for numerical or experimental evaluation of the particle pressure and non-equilibrium osmotic pressure in a dense sheared suspension. Both the friction level between particles and the suspension dilatancy are shown to determine the singularity of the apparent shear viscosity and the flow stability near the jamming transition. The model further predicts a Newtonian behavior for a concentrated suspension of neutrally buoyant particles and no shear thinning behavior in relation with the shear liquefaction of transient solid clusters