7,084 research outputs found
Locking and unlocking of the counterflow transport in nu=1 quantum Hall bilayers by tilting of magnetic field
The counterflow transport in quantum Hall bilayers provided by superfluid
excitons is locked at small input currents due to a complete leakage caused by
the interlayer tunneling. We show that the counterflow critical current
I_c^{CF} above which the system unlocks for the counterflow transport can be
controlled by a tilt of magnetic field in the plane perpendicular to the
current direction. The effect is asymmetric with respect to the tilting angle.
The unlocking is accompanied by switching of the systems from the d.c. to the
a.c. Josephson state. Similar switching takes place for the tunneling set-up
when the current flowing through the system exceeds the critical value I_c^T.
At zero tilt the relation between the tunnel and counterflow critical currents
is I_c^T=2 I_c^{CF}. We compare the influence of the in-plane magnetic field
component B_\parallel on the critical currents I_c^{CF} and I_c^T. The in-plane
magnetic field reduces the tunnel critical current and this reduction is
symmetric with respect to the tilting angle. It is shown that the difference
between I_c^{CF} and I_c^T is essential at field |B_\parallel|\lesssim \phi_0/d
\lambda_J, where \phi_0 is the flux quantum, d is the interlayer distance, and
\lambda_J is the Josephson length. At larger B_\parallel the critical currents
I_c^{CF} and I_c^T almost coincide each other.Comment: 10 pages, 1 fi
Deep-water organic-mineral sediments of the black sea as the object of mining and dewatering
The results of laboratory investigations of grain-size, physical, mechanical and rheological properties of the deep-sea organic-mineral sediments sampled from the depth of 1,920 – 2,150 m at the polygon “Sapropels” in the Black Sea are given. The results obtained are analyzed. The class of particle size distribution and soil category in difficulty of developing for this type of sediments are established.Представлено результати лабораторних досліджень гранулометричного складу, фізикомеханічних та реологічних властивостей глибоководних органо-мінеральних відкладень Чорного моря, відібраних з глибини 1920 – 2150 м на полігоні «Сапропелі». Проведено аналіз отриманих результатів. Визначено клас даного типу відкладень по гранулометричному складу і категорія ґрунту по важкості розробки.Приведены результаты лабораторных исследований гранулометрического состава, физикомеханических и реологических свойств глубоководных органо-минеральных осадков
Черного моря, отобранных с глубины 1920 – 2150 м на полигоне «Сапропели». Проведен
анализ полученных результатов. Определен класс данного типа отложений по гранулометрическому составу и категория грунта по трудности разработки
Phase transformation B1 to B2 in TiC, TiN, ZrC and ZrN under pressure
Phase stability of various phases of MX (M = Ti, Zr; X = C, N) at equilibrium
and under pressure is examined based on first-principles calculations of the
electronic and phonon structures. The results reveal that all B1 (NaCl-type) MX
structures undergo a phase transition to the B2-structures under high pressure
in agreement with the previous total-energy calculations. The B1-MX structures
are dynamically stable under very high pressure (210-570 GPa). The
pressure-induced B2 (CsCl-type) MC phases are dynamically unstable even at high
pressures, and TiN and ZrN are found to crystallize with the B2-structure only
at pressures above 55 GPa. The first-order B1-to-B2 phase transition in these
nitrides is not related to the softening of phonon modes, and the dynamical
instability of B2-MX is associated with a high density of states at the Fermi
level.Comment: 9 pages, 4 figure
Vortex matter and generalizations of dipolar superfluidity concept in layered systems
In the first part of this letter we discuss electrodynamics of an excitonic
condensate in a bilayer. We show that under certain conditions the system has a
dominant energy scale and is described by the effective electrodynamics with
"planar magnetic charges". In the second part of the paper we point out that a
vortex liquid state in bilayer superconductors also possesses dipolar
superfluid modes and establish equivalence mapping between this state and a
dipolar excitonic condensate. We point out that a vortex liquid state in an
N-layer superconductor possesses multiple topologically coupled dipolar
superfluid modes and therefore represents a generalization of the dipolar
superfluidity concept.Comment: v2: references added. v3: discussion extended, references adde
Charge ordering and interlayer phase coherence in quantum Hall superlattices
The possibility of the existence of states with a spontaneous interlayer
phase coherence in multilayer electron systems in a high perpendicular to the
layers magnetic field is investigated. It is shown that phase coherence can be
established in such systems only within individual pairs of adjacent layers,
while such coherence does not exist between layers of different pairs. The
conditions for stability of the state with interlayer phase coherence against
transition to a charge-ordered state are determined. It is shown that in the
system with the number of layers N\leq 10 these conditions are satisfied at any
value of the interlayer distance d. For N>10 there are two intervals of
stability: at sufficiently large and at sufficiently small d. For N\to \infty
the stability interval in the region of small d vanishesComment: 10 page
Superfluidity of electron-hole pairs in randomly inhomogeneous bilayer systems
In bilayer systems electron-hole (e-h) pairs with spatially separated
components (i.e., with electrons in one layer and holes in the other) can be
condensed to a superfluid state when the temperature is lowered. This article
deals with the influence of randomly distributed inhomogeneities on the
superfluid properties of such bilayer systems in a strong perpendicular
magnetic field. Ionized impurities and roughenings of the conducting layers are
shown to decrease the superfluid current density of the e-h pairs. When the
interlayer distance is smaller than or close to the magnetic length, the
fluctuations of the interlayer distance considerably reduce the superfluid
transition temperature.Comment: 13 pages, 3 figure
Competing ideologies of Russia's civil society
Many analysts and public opinion makers in the West conflate the notions of Russia’s non-systemic liberal opposition and the country’s civil society. Indeed, despite garnering the support of a minority of Russia’s population, non-systemic liberal opposition represents a well-organized civic group with a clearly articulated agenda and the ability to take action. Yet, does Russia’s civil society end there? A closer look at the country’s politics shows that Russia has a substantial conservative-traditionalist faction that has also developed agenda for action and formulated opinions. This group is anti-liberal rather than illiberal ideologically and pro-strong state/pro a geopolitically independent Russia rather than pro-Kremlin politically. The interaction between liberal and conservative civic groups represents the battle of meanings, ideas, and ethics, and ultimately determines the future trajectory of Russia’s evolution. Thus, the analysis of Russia’s civil society must represent a rather more nuanced picture than a mere study of the liberal non-systemic opposition. This article will examine the complexity of Russia’s civil society scene with reference to the interplay between the liberal opposition and conservative majority factions. The paper will argue that such complexity stems from ideological value pluralism that falls far beyond the boundaries of the liberal consensus, often skewing our understanding of political practice in Russia
Dynamic equation for quantum Hall bilayers with spontaneous interlayer coherence: The low-density limit
The bilayer systems exhibit the Bose-Einstein condensation of excitons that
emerge due to Coulomb pairing of electrons belonging to one layer with the
holes belonging to the other layer. Here we present the microscopic derivation
of the dynamic equation for the condensate wave function at a low density of
electron-hole () pairs in a strong magnetic field perpendicular to the
layers and an electric field directed along the layers. From this equation we
obtain the dispersion law for collective excitations of the condensate and
calculate the electric charge of the vortex in the exciton condensate. The
critical interlayer spacing, the excess of which leads to a collapse of the
superfluid state, is estimated. In bilayer systems with curved conducting
layers, the effective mass of the pair becomes the function of the
pair coordinates, the regions arise, where the energy of the pair is
lowered (exciton traps), and lastly pairs can gain the polarization in
the basal plane. This polarization leads to the appearance of quantized
vortices even at zero temperature.Comment: 8 page
Kinetic simulations of X-B and O-X-B mode conversion
We have performed fully-kinetic simulations of X-B and O-X-B mode conversion
in one and two dimensional setups using the PIC code EPOCH. We have recovered
the linear dispersion relation for electron Bernstein waves by employing
relatively low amplitude incoming waves. The setups presented here can be used
to study non-linear regimes of X-B and O-X-B mode conversion.Comment: 4 pages, 3 figure
- …