25 research outputs found
Density of States and Conductivity of Granular Metal or Array of Quantum Dots
The conductivity of a granular metal or an array of quantum dots usually has
the temperature dependence associated with variable range hopping within the
soft Coulomb gap of density of states. This is difficult to explain because
neutral dots have a hard charging gap at the Fermi level. We show that
uncontrolled or intentional doping of the insulator around dots by donors leads
to random charging of dots and finite bare density of states at the Fermi
level. Then Coulomb interactions between electrons of distant dots results in
the a soft Coulomb gap. We show that in a sparse array of dots the bare density
of states oscillates as a function of concentration of donors and causes
periodic changes in the temperature dependence of conductivity. In a dense
array of dots the bare density of states is totally smeared if there are
several donors per dot in the insulator.Comment: 13 pages, 15 figures. Some misprints are fixed. Some figures are
dropped. Some small changes are given to improve the organizatio
Complexation of a polyelectrolyte with oppositely charged spherical macroions: Giant inversion of charge
Complexation of a long flexible polyelectrolyte (PE) molecule with oppositely
charged spherical particles such as colloids, micelles, or globular proteins in
a salty water solution is studied. PE binds spheres winding around them, while
spheres repel each other and form almost periodic necklace. If the total charge
of PE is larger than the total charge of spheres, repulsive correlations of PE
turns on a sphere lead to inversion of the net charge of each sphere. In the
opposite case, we predict another correlation effect: under-screened by PE
spheres bind to PE in such a great number that they invert charge of PE. The
inverted charge by absolute value can be larger than the bare charge of PE even
when screening by monovalent salt is weak. At larger concentrations of
monovalent salt, the inverted charge can reach giant proportions. Our theory is
in qualitative agreement with recent experiments on micelles-PE systems.Comment: Various additions and corrections to the text, Figures and
references. Accepted for publication in J. Chem. Phys. 200
Jumps in current-voltage characteristics in disordered films
We argue that giant jumps of current at finite voltages observed in
disordered samples of InO, TiN and YSi manifest a bistability caused by the
overheating of electrons. One of the stable states is overheated and thus
low-resistive, while the other, high-resistive state is heated much less by the
same voltage. The bistability occurs provided that cooling of electrons is
inefficient and the temperature dependence of the equilibrium resistance, R(T),
is steep enough. We use experimental R(T) and assume phonon mechanism of the
cooling taking into account its strong suppression by disorder. Our description
of details of the I-V characteristics does not involve adjustable parameters
and turns out to be in a quantitative agreement with the experiments. We
propose experiments for more direct checks of this physical picture.Comment: Final version, as published; 4 pages, 3 figure
Self-energy limited ion transport in sub-nanometer channels
The current-voltage characteristics of the alpha-Hemolysin protein pore
during the passage of single-stranded DNA under varying ionic strength, C, are
studied experimentally. We observe strong blockage of the current, weak
super-linear growth of the current as a function of voltage, and a minimum of
the current as a function of C. These observations are interpreted as the
result of the ion electrostatic self-energy barrier originating from the large
difference in the dielectric constants of water and the lipid bilayer. The
dependence of DNA capture rate on C also agrees with our model.Comment: more experimental material is added. 4 pages, 7 figure
Statistics of Rare Events in Disordered Conductors
Asymptotic behavior of distribution functions of local quantities in
disordered conductors is studied in the weak disorder limit by means of an
optimal fluctuation method. It is argued that this method is more appropriate
for the study of seldom occurring events than the approaches based on nonlinear
-models because it is capable of correctly handling fluctuations of the
random potential with large amplitude as well as the short-scale structure of
the corresponding solutions of the Schr\"{o}dinger equation. For two- and
three-dimensional conductors new asymptotics of the distribution functions are
obtained which in some cases differ significantly from previously established
results.Comment: 17 pages, REVTeX 3.0 and 1 Postscript figur
Perturbation Theory for the Rosenzweig-Porter Matrix Model
We study an ensemble of random matrices (the Rosenzweig-Porter model) which,
in contrast to the standard Gaussian ensemble, is not invariant under changes
of basis. We show that a rather complete understanding of its level
correlations can be obtained within the standard framework of diagrammatic
perturbation theory. The structure of the perturbation expansion allows for an
interpretation of the level structure on simple physical grounds, an aspect
that is missing in the exact analysis (T. Guhr, Phys. Rev. Lett. 76, 2258
(1996), T. Guhr and A. M\"uller-Groeling, cond-mat/9702113).Comment: to appear in PRE, 5 pages, REVTeX, 2 figures, postscrip
On the Theory of Metal-Insulator Transitions in Gated Semiconductors
It is shown that recent experiments indicating a metal-insulator transition
in 2D electron systems can be interpreted in terms of a simple model, in which
the resistivity is controlled by scattering at charged hole traps located in
the oxide layer. The gate voltage changes the number of charged traps which
results in a sharp change in the resistivity. The observed exponential
temperature dependence of the resistivity in the metallic phase of the
transition follows from the temperature dependence of the trap occupation
number. The model naturally describes the experimentally observed scaling
properties of the transition and effects of magnetic and electric fields.Comment: 4 two-column pages, 4 figures (included in the text