585 research outputs found
Tunable "Doniach Phase Diagram" for strongly-correlated nanoclusters
Exact diagonalization calculations reveal that the energy spacing in
the conduction band tunes the interplay between the {\it local} Kondo and {\it
non local} RKKY interactions, giving rise to a "Doniach phase diagram" for a
nanocluster with regions of prevailing Kondo or RKKY correlations. The parity
of the total number of electrons alters the competition between the Kondo and
RKKY correlations. This interplay may be relevant to experimental realizations
of small rings or quantum dots with tunable magnetic properties. Below a
critical value V of the hybridization the susceptibility exhibits a low-T
exponential activation behavior determined by the interplay of the spin gap and
.Comment: 4 pages, 5 figure
Tuning the magnetism of ordered and disordered strongly-correlated electron nanoclusters
Recently, there has been a resurgence of intense experimental and theoretical
interest on the Kondo physics of nanoscopic and mesoscopic systems due to the
possibility of making experiments in extremely small samples. We have carried
out exact diagonalization calculations to study the effect of energy spacing
in the conduction band states, hybridization, number of electrons, and
disorder on the ground-state and thermal properties of strongly-correlated
electron nanoclusters. For the ordered systems, the calculations reveal for the
first time that tunes the interplay between the {\it local} Kondo and
{\it non local} RKKY interactions, giving rise to a "Doniach phase diagram" for
the nanocluster with regions of prevailing Kondo or RKKY correlations. The
interplay of and disorder gives rise to a versus
concentration T=0 phase diagram very rich in structure. The parity of the total
number of electrons alters the competition between the Kondo and RKKY
correlations. The local Kondo temperatures, , and RKKY interactions depend
strongly on the local environment and are overall {\it enhanced} by disorder,
in contrast to the hypothesis of ``Kondo disorder'' single-impurity models.
This interplay may be relevant to experimental realizations of small rings or
quantum dots with tunable magnetic properties.Comment: 10 pages, 13 figures, to appear in Physics of Spin in Solids:
Materials, Methods, and Applications, (2004
A nonplanar Peierls-Nabarro model and its applications to dislocation cross-slip
A novel semidiscrete Peierls-Nabarro model is introduced which can be used to
study dislocation spreading at more than one slip planes, such as dislocation
cross-slip and junctions. The strength of the model, when combined with ab
initio calculations for the energetics, is that it produces essentiallyan
atomistic simulation for dislocation core properties without suffering from the
uncertainties associated with empirical potentials. Therefore, this method is
particularly useful in providing insight into alloy design when empirical
potentials are not available or not reliable for such multi-element systems. As
an example, we study dislocation cross-slip and constriction process in two
contrasting fcc metals, Al and Ag. We find that the screw dislocation in Al can
cross-slip spontaneously in contrast with that in Ag, where the screw
dislocation splits into two partials, which cannot cross-slip without first
being constricted. The response of the dislocation to an external stress is
examined in detail. The dislocation constriction energy and the critical stress
for cross-slip are determined, and from the latter, we estimate the cross-slip
energy barrier for straight screw dislocations.Comment: Submitted for the Proceedings of Multiscale Modelling of Materials
(London, 2002
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