3,632 research outputs found
Gauge theory description of glass transition
An analytical approach, which develops the gauge model of the glass
transition phenomenon, is suggested. It is based on the quantum field theory
and critical dynamics methods. The suggested mechanism of glass transition is
based on the interaction of the local magnetization field with the massive
gauge field, which describes frustration-induced plastic deformation. The
example of the three-dimensional Heisenberg model with trapped disorder is
considered. It is shown that the glass transition appears when the fluctuations
scale reaches the frustrations scale, and the mass of the gauge field becomes
equal to zero. The Vogel-Fulcher-Tammann relation for the glass transition
kinetics and critical exponent for non-linear susceptibility, , are derived in the framework of the suggested approach.Comment: 4 pages, 4 figures; Added references; correction
Gauge theory approach to glass transitions
This theory combines a thermodynamic approach with a dynamic one in order to
describe glass transition. Glass transition is regarded as an inaccessible
second order phase transition, which is interrupted because of premature
critical slowing down, caused by the system's frustration. The
frustration-induced vortices are present in the structure besides
thermoactivated vortices, and prevent the development of the order parameter
fluctuations, that leads to the critical slowing down the system kinetics at
some temperature above the phase transition point
Single particle Green's functions and interacting topological insulators
We study topological insulators characterized by the integer topological
invariant Z, in even and odd spacial dimensions. These are well understood in
case when there are no interactions. We extend the earlier work on this subject
to construct their topological invariants in terms of their Green's functions.
In this form, they can be used even if there are interactions. Specializing to
one and two spacial dimensions, we further show that if two topologically
distinct topological insulators border each other, the difference of their
topological invariants is equal to the difference between the number of zero
energy boundary excitations and the number of zeroes of the Green's function at
the boundary. In the absence of interactions Green's functions have no zeroes
thus there are always edge states at the boundary, as is well known. In the
presence of interactions, in principle Green's functions could have zeroes. In
that case, there could be no edge states at the boundary of two topological
insulators with different topological invariants. This may provide an
alternative explanation to the recent results on one dimensional interacting
topological insulators.Comment: 16 pages, 2 figure
Magneto-polarisability of mesoscopic rings
We calculate the average polarisability of two dimensional mesoscopic rings
in the presence of an Aharonov-Bohm flux. The screening is taken into account
self-consistently within a mean-field approximation. We investigate the effects
of statistical ensemble, finite frequency and disorder. We emphasize
geometrical effects which make the observation of field dependent
polarisability much more favourable on rings than on disks or spheres of
comparable radius. The ratio of the flux dependent to the flux independent part
is estimated for typical GaAs rings.Comment: pages, Revtex, 1 eps figur
Phi_0 - Periodic Aharonov-Bohm Oscillations Survive Ensemble Averaging
We have demonstrated that Phi_0 periodic Aharonov--Bohm oscillations measured
in a ensemble of rings may survive after ensemble averaging procedure. The
central point is the difference between the preparation stage of the ensemble
and the subsequent measurement stage. The robustness of the effect under finite
temperature and non--zero charging energy of rings is discussed.Comment: 11 pages, 2 figures, RevTex 3.0,WIS-93/84/Aug.-P
Quantum interference and Coulomb interaction in arrays of tunnel junctions
We study the electronic properties of an array of small metallic grains
connected by tunnel junctions. Such an array serves as a model for a granular
metal. Previous theoretical studies of junction arrays were based on models of
quantum dissipation which did not take into account the diffusive motion of
electrons within the grains. We demonstrate that these models break down at
sufficiently low temperatures: for a correct description of the screening
properties of a granular metal at low energies the diffusive nature of the
electronic motion within the grains is crucial. We present both a diagrammatic
and a functional integral approach to analyse the properties of junction
arrays. In particular, a new effective action is obtained which enables us to
describe the array at arbitrary temperature. In the low temperature limit, our
theory yields the correct, dynamically screened Coulomb interaction of a normal
metal, whereas at high temperatures the standard description in terms of
quantum dissipation is recovered.Comment: 14 pages, 7 figure
Bloch oscillations in one-dimensional spinor gas
A force applied to a spin-flipped particle in a one-dimensional spinor gas
may lead to Bloch oscillations of particle's position and velocity. The
existence of Bloch oscillations crucially depends on the viscous friction force
exerted by the rest of the gas on the spin excitation. We evaluate the friction
in terms of the quantum fluid parameters. In particular, we show that the
friction is absent for integrable cases, such as SU(2) symmetric gas of bosons
or fermions. For small deviations from the exact integrability the friction is
very weak, opening the possibility to observe Bloch oscillations.Comment: 4 pages, 2 figure
Wigner-Dyson Statistics from the Keldysh Sigma-Model
The level statistics of disordered metallic grains with broken time reversal
invariance is obtained from a saddle point analysis of the Keldysh nonlinear
sigma-model
Electron Transport in Granular Metals
We consider thermodynamic and transport properties of a long granular array
with strongly connected grains (inter-grain conductance g>>1.) We find that the
system exhibits activated behavior of conductance and thermodynamic density of
states ~exp(-T*/T) where the gap, T*, is parametrically larger than the energy
at which conventional perturbation theory breaks down. The scale T* represents
energy needed to create a long single-electron charge soliton propagating
through the array.Comment: 4 pages, 1 figur
A novel graph decomposition approach to the automatic processing of poorly formalized data : innovative ideas : a management case study
In the following paper we present a novel approach to unstructured data processing by imposing a hierarchical graph-based structure on the data and decomposing it into separate subgraphs according to optimization criteria. In the scope of the paper we also consider the problem of automatic classification of textual data for the synthesizing the hierarchical data structure. The proposed approach uses textual information on the first stage to classify ideas, innovations, and objects of intellectual property (OIPs) to construct a multilayered graph. Numerical criteria are used to decompose constructed graph into separate subgraphs. In the scope of the research we apply the developed approach to the innovative ideas in a management case study. The research has been conducted in the scope of a joint research project with financial aid of Ministry of Education and Science of Russian Federation RFMEFI57314X0007.peer-reviewe
- …