Publication Numbers: 42.
In this project we examine the glassy properties
of
strongly disordered systems of localized electrons,
interacting via the Coulomb interaction.
These studies are motivated by recent experimental
results obtained by the group of Zvi Ovadyahu
in
Jerusalem, who observed very slow relaxation
times
characteristic of glassy dynamics.
Theoretical studies have shown
the existence of multiple low energy minima in
such models,
which is typical in glassy systems.
The glassy behavior sets in gradually as the
temperature is
lowered without evidence for
a finite temperature glass transition.
Theoretical studies and computer simulations
have
shown that there is a gap in the density
of states (DS) around the Fermi level, known
as the
Coulomb gap.
The statistical physics of Coulomb Glass systems
is
poses challenging problems since one needs to
include
the long range Coulomb interaction
while constraining the motion of electrons by
variable range hopping considerations.
Introducing a set of suitable correlation functions
we have recently studied the equilibrium dynamics
of the Coulomb glass at low temperatures [42].
We found
that the configuration of occupied sites within
the
Coulomb gap persistently changes at temperatures
much
lower than the width of the gap itself,
while the shape of the density of states
remains essentially unchanged.
We interpret these results in terms of drift
of the
system between multiple energy minima, which
may also
imply that interacting electrons may be effectively
delocalized within the Coulomb gap.
Future Plans:
We now focus on
extending our approach to non-equilibrium conditions
in which the challenge is to calculate the conductivity.
Without the Coulomb interaction, the conductivity
can
be described as a percolation problem.
However, the Coulomb interaction introduces a
varying
energy landscape, deviating from the percolation
picture,
while the variable range hopping introduces a
vast
increase in the number of possible hopping paths.
A direct calculation of the conductivity will
help
us to develop a theoretical framework for the
understanding of the experimental results, in
which
the system is driven out of equilibrium and
the conductivity is measured during the equilibration
process.