89 research outputs found
Polarization properties of polymer-based photonic crystal fibers
Selectively filled photonic crystal fibers with polydimethylsiloxane (PDMS), a silicon-type material, have been studied. Is has been demonstrated that polarization properties of these hybrid devices and the properties of the guided light in relation with the temperature changes, finding that the state of polarization (SOP) change with the increasing temperature but remains constant for a wide spectrum of wavelengths for a determinate temperature
Dynamical scaling of the quantum Hall plateau transition
Using different experimental techniques we examine the dynamical scaling of
the quantum Hall plateau transition in a frequency range f = 0.1-55 GHz. We
present a scheme that allows for a simultaneous scaling analysis of these
experiments and all other data in literature. We observe a universal scaling
function with an exponent kappa = 0.5 +/- 0.1, yielding a dynamical exponent z
= 0.9 +/- 0.2.Comment: v2: Length shortened to fulfil Journal criteri
Conductance spectra of (Nb, Pb, In)/NbP -- superconductor/Weyl semimetal junctions
The possibility of inducing superconductivity in type-I Weyl semimetal
through coupling its surface to a superconductor was investigated. A single
crystal of NbP, grown by chemical vapor transport method, was carefully
characterized by XRD, EDX, SEM, ARPES techniques and by electron transport
measurements. The mobility spectrum of the carriers was determined. For the
studies of interface transmission, the (001) surface of the crystal was covered
by several hundred nm thick metallic layers of either Pb, or Nb, or In. DC
current-voltage characteristics and AC differential conductance through the
interfaces as a function of the DC bias were investigated. When the metals
become superconducting, all three types of junctions show conductance increase,
pointing out the Andreev reflection as a prevalent contribution to the subgap
conductance. In the case of Pb-NbP and Nb-NbP junctions, the effect is
satisfactorily described by modified Blonder-Tinkham-Klapwijk model. The
absolute value of the conductance is much smaller than that for the bulk
crystal, indicating that the transmission occurs through only a small part of
the contact area. An opposite situation occurs in In-NbP junction, where the
conductance at the peak reaches the bulk value indicating that almost whole
contact area is transmitting and, additionally, a superconducting proximity
phase is formed in the material. We interpret this as a result of indium
diffusion into NbP, where the metal atoms penetrate the surface barrier and
form very transparent superconductor-Weyl semimetal contact inside. However,
further diffusion occurring already at room temperature leads to degradation of
the effect, so it is observed only in the pristine structures. Despite of this,
our observation directly demonstrates possibility of inducing superconductivity
in a type-I Weyl semimetal.Comment: Accepted for Phys. Rev. B. 13 pages, 12 figures. Second version with
major revisions. The title was changed. One author R. Jakiela added. New
inset to Fig. 8(A). New fits in Fig. 8 (B) and Fig. 10 (B). Added figures 12
(C)-(E). Added Fig. 12 (F) with SIMS data. Rewritten chapters III-C-2 and
III-C-3. Reference no. 38 removed, 11 new references: 9, 21, 22, 40-44, 46-49
were adde
Topological crystalline insulator states in Pb(1-x)Sn(x)Se
Topological insulators are a novel class of quantum materials in which
time-reversal symmetry, relativistic (spin-orbit) effects and an inverted band
structure result in electronic metallic states on the surfaces of bulk
crystals. These helical states exhibit a Dirac-like energy dispersion across
the bulk bandgap, and they are topologically protected. Recent theoretical
proposals have suggested the existence of topological crystalline insulators, a
novel class of topological insulators in which crystalline symmetry replaces
the role of time-reversal symmetry in topological protection [1,2]. In this
study, we show that the narrow-gap semiconductor Pb(1-x)Sn(x)Se is a
topological crystalline insulator for x=0.23. Temperature-dependent
magnetotransport measurements and angle-resolved photoelectron spectroscopy
demonstrate that the material undergoes a temperature-driven topological phase
transition from a trivial insulator to a topological crystalline insulator.
These experimental findings add a new class to the family of topological
insulators. We expect these results to be the beginning of both a considerable
body of additional research on topological crystalline insulators as well as
detailed studies of topological phase transitions.Comment: v2: published revised manuscript (6 pages, 3 figures) and
supplementary information (5 pages, 8 figures
Development of an eight-band theory for quantum-dot heterostructures
We derive a nonsymmetrized 8-band effective-mass Hamiltonian for quantum-dot
heterostructures (QDHs) in Burt's envelope-function representation. The 8x8
radial Hamiltonian and the boundary conditions for the Schroedinger equation
are obtained for spherical QDHs. Boundary conditions for symmetrized and
nonsymmetrized radial Hamiltonians are compared with each other and with
connection rules that are commonly used to match the wave functions found from
the bulk kp Hamiltonians of two adjacent materials. Electron and hole energy
spectra in three spherical QDHs: HgS/CdS, InAs/GaAs, and GaAs/AlAs are
calculated as a function of the quantum dot radius within the approximate
symmetrized and exact nonsymmetrized 8x8 models. The parameters of dissymmetry
are shown to influence the energy levels and the wave functions of an electron
and a hole and, consequently, the energies of both intraband and interband
transitions.Comment: 36 pages, 10 figures, E-mail addresses: [email protected],
[email protected]
Modeling and Experimental Verification of a Prediction Algorithm for Controlling an Active Power Filter
В данной статье рассмотрен вопрос улучшения качества тока в трехфазной распределительной сети с использованием активного силового фильтра. Приведена структура системы управления активным силовым фильтром, реализующая прогнозирующий алгоритм. Представлены результаты имитационного моделирования активного силового фильтра на базе трехфазного трехуровнего инвертора напряжения. Проведено исследование прототипа активного силового фильтра на экспериментальной установке.In this paper, the problem of power quality improvement in the three-phase distribution network using an active power filter is considered. The structure of the control system of the active power filter is outlined. Modeling results of the power filter based on a three-phase three-level voltage inverter are presented. The performance of the active power filter has been tested using an experimental set-up. The results of modeling have been successfully verified experimentally.Исследование выполнено при финансовой поддержке РФФИ и Правительства Новосибирской области в рамках научного проекта № 17-48-543169
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