398 research outputs found
Native ultrametricity of sparse random ensembles
We investigate the eigenvalue density in ensembles of large sparse Bernoulli
random matrices. We demonstrate that the fraction of linear subgraphs just
below the percolation threshold is about 95\% of all finite subgraphs, and the
distribution of linear chains is purely exponential. We analyze in detail the
spectral density of ensembles of linear subgraphs, discuss its ultrametric
nature and show that near the spectrum boundary, the tail of the spectral
density exhibits a Lifshitz singularity typical for Anderson localization. We
also discuss an intriguing connection of the spectral density to the Dedekind
-function. We conjecture that ultrametricity is inherit to complex
systems with extremal sparse statistics and argue that a number-theoretic
ultrametricity emerges in any rare-event statistics.Comment: 24 pages, 9 figure
Rashba split surface states in BiTeBr
Within density functional theory, we study bulk band structure and surface
states of BiTeBr. We consider both ordered and disordered phases which differ
in atomic order in the Te-Br sublattice. On the basis of relativistic ab-initio
calculations, we show that the ordered BiTeBr is energetically preferable as
compared with the disordered one. We demonstrate that both Te- and
Br-terminated surfaces of the ordered BiTeBr hold surface states with a giant
spin-orbit splitting. The Te-terminated surface-state spin splitting has the
Rashba-type behavior with the coupling parameter \alpha_R ~ 2 eV\AA.Comment: 8 pages, 7 figure
Spin-helical Dirac states in graphene induced by polar-substrate surfaces with giant spin-orbit interaction: a new platform for spintronics
Spintronics, or spin electronics, is aimed at efficient control and
manipulation of spin degrees of freedom in electron systems. To comply with
demands of nowaday spintronics, the studies of electron systems hosting giant
spin-orbit-split electron states have become one of the most important
directions providing us with a basis for desirable spintronics devices. In
construction of such devices, it is also tempting to involve graphene, which
has attracted great attention because of its unique and remarkable electronic
properties and was recognized as a viable replacement for silicon in
electronics. In this case, a challenging goal is to make graphene Dirac states
spin-polarized. Here, we report on absolutely new promising pathway to create
spin-polarized Dirac states based on coupling of graphene and polar-substrate
surface states with giant Rashba-type spin-splitting. We demonstrate how the
spin-helical Dirac states are formed in graphene deposited on the surface of
BiTeCl. This coupling induces spin separation of the originally spin-degenerate
graphene states and results in fully helical in-plane spin polarization of the
Dirac electrons.Comment: 5 pages, 3 figure
First principles quasiparticle damping rates in bulk lead
First principles calculations of the damping rates (inverse inelastic
lifetimes) of low energy quasiparticles in bulk Pb are presented. Damping rates
are obtained both for excited electrons and holes with energies up to 8 eV on a
set of k vectors throughout the Brillouin zone (BZ). Strong localization
effects in the calculated lifetimes are found. Averaged over the BZ inelastic
lifetimes versus quasiparticle energy are reported as well. In addition, the
effect of the spin-orbit induced splitting in the band structure on the
calculated lifetimes in Pb is investigated.Comment: 10 pages, 8 figures, 5 table
Many-body effects on the Rashba-type spin splitting in bulk bismuth tellurohalides
We report on many-body corrections to one-electron energy spectra of bulk
bismuth tellurohalides---materials that exhibit a giant Rashba-type spin
splitting of the band-gap edge states. We show that the corrections obtained in
the one-shot approximation noticeably modify the spin-orbit-induced spin
splitting evaluated within density functional theory. We demonstrate that
taking into account many-body effects is crucial to interpret the available
experimental data.Comment: 6 pages, 1 figur
Formation of a single innovation space in the agrarian sector of the EAEU Member States
The relevance of the study is determined by the need to form a single innovative space in the agricultural sector of the EAEU Member States in order to make rational use of the aggregate scientific potential of the countries of the Union.
Models of interstate cooperation in the scientific and technical sphere were developed and a “panel of indicators” for the development of the market for scientific and technical products was proposed.
Practical recommendations on the transfer of innovations in the agricultural sector of the economy of the EAEU member states are given.peer-reviewe
Pressure on charged domain walls and additional imprint mechanism in ferroelectrics
The impact of free charges on the local pressure on a charged ferroelectric
domain wall produced by an electric field has been analyzed. A general formula
for the local pressure on a charged domain wall is derived considering full or
partial compensation of bound polarization charges by free charges. It is shown
that the compensation can lead to a very strong reduction of the pressure
imposed on the wall from the electric field. In some cases this pressure can be
governed by small nonlinear effects. It is concluded that the free charge
compensation of bound polarization charges can lead to substantial reduction of
the domain wall mobility even in the case when the mobility of free charge
carriers is high. This mobility reduction gives rise to an additional imprint
mechanism which may play essential role in switching properties of
ferroelectric materials. The effect of the pressure reduction on the
compensated charged domain walls is illustrated for the case of 180-degree
ferroelectric domain walls and of 90-degree ferroelectric domain walls with the
head-to-head configuration of the spontaneous polarization vectors.Comment: subm. to PRB. This verion is extended by appendi
On scale-free and poly-scale behaviors of random hierarchical network
In this paper the question about statistical properties of
block--hierarchical random matrices is raised for the first time in connection
with structural characteristics of random hierarchical networks obtained by
mipmapping procedure. In particular, we compute numerically the spectral
density of large random adjacency matrices defined by a hierarchy of the
Bernoulli distributions on matrix elements, where
depends on hierarchy level as (). For the spectral density we clearly see the free--scale
behavior. We show also that for the Gaussian distributions on matrix elements
with zero mean and variances , the tail of the
spectral density, , behaves as for and , while for
the power--law behavior is terminated. We also find that the vertex
degree distribution of such hierarchical networks has a poly--scale fractal
behavior extended to a very broad range of scales.Comment: 11 pages, 6 figures (paper is substantially revised
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