
Research Highlights
Nanomechanical Shuttling in Coulomb Blockade Structures 
Mechanical degrees of freedom take on a primary role in the charge transfer process
in many singleelectron devices, where transport is controlled by quantummechanical
tunneling and Coulomb interactions and where parameters of a tunnel barrier can be
modified by mechanical motion. A typical system of this kind is a single electron transistor (SET)
with a deformable tunnel barrier, the so called NanoElectroMechanical SET (NEMSET).
A new kind of electron transport in this and other types of nanodevices is referred
to as "shuttle transport" of electrons and means that electrons are transferred
between the metallic leads via a movable smallsized island.
[more information.....]
 
Microscopic theory of thermal phase slips in clean narrow superconducting wires 
Finite resistivity in superconducting wires appears due to phase slip events: local abrupt switches of the
system between its metastable states accompanied by phase jumps
discontinuously by 2π, as illustrated by the animation. The resistivity is mainly determined by the energy barrier for such an event.
For a clean onechannel wire it is possible to find exact analytical
solution for the energy barrier valid in the whole temperature and current range.
[more information.....]
 
SelfAssembled Magnetic Surface Swimmers 
We report studies of a novel type of selfassembled magnetically actuated surface swimmers (magnetic snakes),
formed from a dispersion of magnetic microparticles on the liquid/air interface and energized by an alternating magnetic field.
We show that under certain conditions the snakes spontaneously break the symmetry of surface flows and turn into selfpropelled objects.
Parameters of the driving magnetic field tune the propulsion velocity of these snakelike swimmers.
We find that the surface flows symmetry can be also broken in a controlled fashion by attaching a large bead to a magnetic snake (beadsnake hybrid),
transforming it into a robust selflocomoting entity.
Observed phenomena have been successfully described by developed phenomenological model based on the amplitude equation for surface waves
coupled to the largescale hydrodynamic mean flow equation.
[more information.....]
 
Collective alignment of polar filaments by molecular motors 
We study the alignment of polar biofilaments, such as microtubules and actin,
subject to the action of multiple molecular motors attached simultaneously to more than one filament.
Focusing on a paradigm model of only two filaments interacting with multiple motors,
we were able to investigate in detail the alignment dynamics.
While almost no alignment occurs in the case of a single motor,
the filaments become rapidly aligned due to the collective action of the motors.
Our analysis shows that the alignment time is governed by the number of bound motors
and the magnitude of the motor force fluctuations.
We demonstrate that the timescale of alignment is in the order of seconds,
much faster than for passive crosslinkinduced bundling.
in vitro experiments on multiplemotor alignment of microtubules
are in good agreement with these results. [more information.....]
 
Hopping transport in granular metals and superconductors 
Arrays of metallic granules, granular metals, are in the insulating phase at low temperatures if the
coupling between granules is weak and exhibit stretched exponential conductivity behavior σ∝exp((T_{0}/T)^{1/2}), resembling
EfrosShklovskii hopping conductivity in semiconductors. This temperature dependence observed not only
in numerous experiments on disordered granular metals but, strikingly, also in perfectly periodic arrays
of metallic granules and periodic arrays of semiconductor quantum dots without visible traces of disorder
posed a fundamental problem that resisted almost three decade long intense attacks of theorists.
In our recent work [1] we explain the observed dependence in terms of the MottEfrosShklovskiilike variable
range hopping mechanism. Our approach includes two key ingredients: (i) electrostatic disorder induced on the
granules by the charged centers imbedded in dielectric matrix of granular conductors and (ii) the theory of
coherent cotunneling through the chain of granules providing mechanism for the electron hopping over several
granules. [more information.....]
[1] 
Granular electronic systems,
I. S. Beloborodov, A. V. Lopatin, V. M. Vinokur, and K. B. Efetov,
Rev. Mod. Phys., 79, 469 (2007). 
[2] 
Coulomb effects and hopping transport in granular metals ,
I. S. Beloborodov, A. V. Lopatin, and V. M. Vinokur,
Phys. Rev. B, 72, 125121 (2005). 
 (click to play animations)

A new method for random number generation 
Many researches in a rich variety of sciences, including quantum, statistical, and nuclear physics,
quantum chemistry, material science, and many others, rely heavily in their research on the use of
random numbers. The most efficient way of generating sequences of random numbers is based on deterministic
recursive rules, which produce pseudorandom numbers. The design of the incrementally powerful random number
generators (RNG) that behave as realizations of independent uniformly distributed random variables and
approximate "true randomness" [1] remains one of the major challenges for computational science.
A new method for constructing highquality pseudorandom numbers generators (RNG) developed by Lev Barash and
Lev Shchur [2] marks a breakthrough in the field. Traditionally, random numbers (RN) are the coordinates of
some periodic trajectory, and correlations exist both along the trajectory and between bits of the given number.
The proposed approach to making numbers less correlated is to generate an ensemble of uncorrelated trajectories,
and use one bit (represented by two digits 0 and 1) from the position of each trajectory to construct sbit
number from s coordinates. Generation of the ensemble of trajectories is naturally parallel computation.
The series of generators are developed using new method with the efficient realizations for Pentium processors,
making our RNGs competitive with the best known generators. Generators were tested with the battery of calibrated
sets of tests. [more information.....]
[1] 
The art of the computer programming, Vol. 2 ,
D. Knuth, (AddisonWesley, Cambridge, 1981) 
[2] 
L. Barash and L.N. Shchur,
Periodic orbits of the ensemble of SinaiArnold cat maps and pseudorandom number generation,
Phys. Rev. E 73, 036701 (2006). [physics/0409069.] 
 
Nondemolition measurements of a single quantum spin using Josephson oscillations 
Quantum measurements in mesoscopic systems by use of tunneling
attracted recently great interest, due to the challenges of both
the single spin detection and quantum computing where the final
state of a qubit after computation must be measured. We showed
that quantum nondemolition (QND) measurements of the spin
projection on the direction of the applied magnetic field are
possible with the use of spindependent Josephson tunneling at low
temperatures when effects of quasiparticles are negligible. [more information.....]
 
Full counting statistics of a charge shuttle 
Current flowing in a nanograin that can oscillate between two leads induces vibration of the grain itself.
The resulting current voltage characteristics can differ substantially from the static case. In particular
the oscillations of the grain can become so large and regular that electrons can jump in or out of the central
grain only when the grain is near one of the two leads. In this regime the current flowing through the system
becomes proportional to the frequency of oscillation. In this work not only the average current transmitted, but
all current cumulants have been considered (Full counting statistics). Its knowledge allows to understand better
charge transfer dynamics. A strong reduction of the Fano factor together with an asymmetric distribution of
transmitted charges have been found. [more information.....]
 
Transport Properties of Granular Metals 
Granular metals exhibit a wealth of behaviors generic to strongly
interacting disordered electronic systems and offer a unique
experimental tool for studying the interplay between the effects
of disorder and interactions. Depending on the strength of
coupling between the grains these systems can assume either
insulating or metallic phases. [more information.....]
 
Josephson vortices and solitons inside pancake vortex lattice in layered superconductors 
In very anisotropic layered superconductors tilted magnetic field
generates two interpenetrating vortex sublattices. This set of
crossing lattices contains a sublattice of Josephson vortices and a sublattice
of pancakevortex stacks. Due to competing energy and length scales crossing
vortex lattices have very rich spectrum of interesting properties. In
particular, the pancakevortex sublattice modifies structure of the
Josephson vortex in a very unusual way. [more information.....]
 
Vortex state excitations in soft magnetic submicronsize elements 
Submicron magnetic elements with regular shapes (rectangular, cylindrical etc.) attracted much attention
during the last years due to considerable progress in the elements' preparation and characterization. Spatial
confinement and finitesize effects alter essentially magnetic properties of the elements. These effects are
critically important for new technological applications, such as patterned magnetic media, memory cells, spintronics
devices etc. Thus, it is necessary to have an adequate theoretical description of magnetic properties of individual patterned
elements, which will be combined into more complex structures such as twodimensional arrays, multilayer elements etc.
The magnetization distribution within a magnetic element in zero field depends on its size and shape. The interplay of finite
size and shapeinduced modifications of magnetic behavior of small elements leads to variety of their static and dynamic properties.
The competition between different energies results, in general, in some nonuniform magnetic states. The curlingtype or vortex
magnetization state is a ground state of ferromagnetic diskshaped submicron elements. [more information.....]
[1] 
Eigenfrequencies of vortex state excitations in magnetic submicronsize disks,
K.Y. Guslienko, B.A. Ivanov, V. Novosad et al.,
J. Appl. Phys. 91, 8037 (2002). 
[2] 
Spin excitations of magnetic vortices in ferromagnetic nanodots,
V. Novosad, M. Grimsditch, K.Y. Guslienko et al.,
Phys. Rev. B 66, 052407 (2002). 
 
Domain wall superconductivity in hybrid superconductorferromagnet structures 
The hybrid superconductorferromagnet (S/F) systems give an interesting example of magnetism and superconductivity
interplay with an important potential for practical applications. The presence of the domain wall is inherent to all
ferromagnets of macroscopical sizes, and so the question of influence of the domain structure on the superconducting
characteristic of S/F structures arises. Depending on the parameters of domain structure superconductivity may be
enhanced or suppressed in the region near the domain wall. The displacement of the domain wall by the external magnetic
field could produce the motion of the superconducting channel in S layer. [more information.....]
 
Quantumlevel resolved Coulomb blockade 
The phenomenon of the Coulomb
blockade has been ubiquitous in solid state physics. It is a manifestation of
the fact that electron occupying a restricted region in space ( e.g. a
quantum dot) blockades the passage of other electrons, owing to electrostatic
interaction. We have found that transport and spectral properties of quantum dots
depend crucially on the relative signs of the couplings of (consecutive) dot's
levels to the external leads. [more information.....]
 
Nanoscale superconductor as a ballistic quantum switch 
A rich variety of vortex structures appear in mesoscopic superconductors in which only a few quanta of magnetic
flux are trapped. The quasiparticle excitations in the vortices form coherent quantummechanical states that
offer the possibility of controlling the phasecoherent transport through the sample by changing the number of
trapped flux quanta and their configuration. [more information.....]


Magnetic flux instabilities in typeII superconductors 
The formation of a macroscopic currentcarrying critical state in type II
superconductors occurs via penetration of the magnetic flux front of pinned
vortices from the surface of the sample. Recent advances in the magnetooptical
imaging have revealed puzzling instabilities of the critical state, including
magnetic macroturbulence, kinetic front roughening, magnetic avalanches and
dendritictype instabilities. These phenomena display remarkable similarities
with other dendritic structures in crystal growth, nonequilibrium chemical and
biological systems, and crack propagation. [more information.....]
 
Largescale flow formation in ensembles of swimming bacteria 
We conduct experimental and theoretical studies of selforganization
of concentrated
ensembles of swimming bacteria Bacilus Subtilis. Experiments
are performed in a very thin (of the order of 1 bacterium
diameter) fluid film spanned between four supporting fibers. Small
amplitude electric field is used to adjust dynamically the
density of bacteria inside the experimental cell. We also develop
mathematical model of hydrodynamicallyinduced
selforganization of concentrated ensembles of swimming bacteria in thin
fluid film. [more information.....]
 


