Transport through a constriction in a FQH-annulus

The flux periodicity of thermodynamic properties of an annulus in the fractional quantum Hall state with a constriction is considered. It is found that -periodicity is obtained due to transfer of fractionally charged particles or composite fermions between the edges of the annulus, respectively. The result for the finite magnitude of the persistent current across a very strong constriction is presented, as obtained with an extension of Wen’s edge state theory.     

Properties of Josephson junctions in the inhomogeneous magnetic field of a system of ferromagnetic particles

The effect of a system of ferromagnetic particles on the field-dependent critical current of a Josephson junction is experimentally studied for junctions of different geometries. For edge junctions, the effect of commensurability between the periodic magnetic field of the particles and the Josephson vortex lattice is observed. The effect manifests itself in additional maxima of the field-dependent critical current. For overlap junctions, giant (greater than sixfold) variations of the maximum critical current are observed depending on the magnetic state of the particles. The changes in the “Fraunhofer” pattern of the overlaped Josephson junctions are attributed to the formation of Abrikosov vortices due to the effect of uniformly magnetized particles. The effects revealed in the experiments can be used to analyze the inhomogeneous magnetic field of a system of submicron particles and to control the transport properties of Josephson junctions.     

Shot noise of a mesoscopic two-particle collider

We investigate the shot noise generated by particle emission from a mesoscopic capacitor into an edge state coupled to another edge state at a quantum point contact (QPC). For a capacitor subject to a periodic voltage the resulting shot noise is proportional to the number of particles (both electrons and holes) emitted during a period. The shot noise is proportional to the driving frequency, however it is independent of the applied voltage. If two capacitors are coupled to a QPC at different sides then the resulting shot noise is maximally the sum of noises produced by each of the capacitors. However, the noise is suppressed if particles of the same kind are emitted simultaneously.     

Relaxation of the edge atoms of a stepped Cu(410) surface

The edge atom position of the stepped Cu(410) surface has been investigated with low energy ion scattering (LEIS) using 10–20 keV H⁺. It is possible to determine the atomic position by utilizing atomic shadowing effects. The scattered particles are analysed with a time-of-flight spectrometer. This means that we can detect scattered hydrogen leaving the copper surface in the neutral state as well as in the charged state, so the influence of neutralization of the scattered particles along different outgoing trajectories is eliminated. We find an inward relaxation of the edge atoms; assuming that this relaxation takes place in the (100) plane it amounts to about 8% of the interlayer spacing.     

Persistent currents in a graphene ring with armchair edges

A graphene nanoribbon with armchair edges is known to have no edge state. However, if the nanoribbon is in the quantum spin Hall state, then there must be helical edge states. By folding a graphene ribbon into a ring and threading it by a magnetic flux, we study the persistent charge and spin currents in the tight-binding limit. It is found that, for a broad ribbon, the edge spin current approaches a finite value independent of the radius of the ring. For a narrow ribbon, inter-edge coupling between the edge states could open the Dirac gap and reduce the overall persistent currents. Furthermore, by enhancing the Rashba coupling, we find that the persistent spin current gradually reduces to zero at a critical value beyond which the graphene is no longer a quantum spin Hall insulator.     

Effect of initial ion distribution and electron relaxation of plasma on transient characteristic of a plane Langmuir probe

The transient characteristics of a plane Langmuir probe for the case of an equilibrium distribution of the plasma particles were obtained by integration of the equations of motion of test particles. The conditions in which the transient characteristic has two peaks were determined. The first peak is due to ions whose initial velocity is directed towards the probe, and the second to ions whose initial velocity is directed away from the probe. The effect of electron relaxation on the leading edge of the probe current pulse was investigated. A relation connecting the plasma ion temperature with the lag of the probe current maximum is obtained.Dnepropetrovsk State University in Commemoration of the 300th Anniversary of Reunion of the Ukraine with Russia.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 37–40, August, 1978.     

Strong correlations in a model of a gauged (2+1)-dimensional nonlinear Schrödinger equation

Phenomena caused by strong correlations between nonlinear modes in planar systems are briefly reviewed. The analysis is restricted to the model of a nonlinear Schrödinger equation. Stationary field distributions are found. The number of particles is obtained as a function of a parameter characterizing the degree of linking of the world lines of excitations. It is shown that, for small values of this parameter, a two-dimensional lattice is characterized by universal attraction, which can be a dynamical cause for the transition to the coherent state. The relation between the chiral nonlinear edge modes and breaking of the Galilei invariance in the system under consideration is discussed.     

Ab initio study of field emission from graphitic ribbons

We have performed first-principles calculations on field emission (FE) from graphitic ribbons within the time-dependent density-functional theory. An important finding is that dangling bond states localized at clean edges are major contributors to FE current. H termination makes the FE current small due to the disappearance of the dangling-bond states. FE is found not to occur from the edge state of a H-terminated zigzag ribbon even when the state is at the Fermi level. The results of the FE current from graphitic ribbons give approximately 1 microA for maximum of FE current from a circular edge of graphitic sheets with approximately 1 nm diameter of an open-ended multiwalled carbon nanotube under a high electric field of approximately 1 V/A.     

Electrical readout of the local nuclear polarization in the quantum Hall effect: a hyperfine battery

It is demonstrated that the now well-established "flip-flop" mechanism of spin exchange between electrons and nuclei in the quantum Hall effect can be reversed. We use a sample geometry which utilizes separately contacted edge states to establish a local nuclear spin polarization--close to the maximum value achievable--by driving a current between electron states of different spin orientation. When the externally applied current is switched off, the sample exhibits an output voltage of up to a few tenths of a mV, which decays with a time constant typical for the nuclear spin relaxation. The surprising fact that a sample with a local nuclear spin polarization can act as a source of energy and that this energy is well above the nuclear Zeeman splitting is explained by a simple model which takes into account the effect of a local Overhauser shift on the edge state reconstruction.     

Mathematical Modeling of the Interaction of a Shock Wave with a Dense Cloud of Particles within the Framework of the Two-Fluid Approach

A parametric numerical study of the interaction of a shock wave with a dense cloud of particles is performed. The problem is solved in the framework of the two-fluid approach, with both the gas and dispersed phases are considered compressible media non-equilibrium in velocity and pressure. The system of governing hyperbolic equations was numerically solved using the Harten–Lax–van Leer method. The statement of the problem corresponds to the arrangement of natural experiments. The simulations revealed the main features of the process, such as the formation of transmitted and reflected waves, the movement of the cloud with a steep leading edge and a smeared tailing edge. The amplitudes of the transmitted and reflected waves, as well as the dynamics of the motion of the cloud, are compared to those observed in real experiments. The influence of the parameters of the equation of state of the dispersed phase and some properties of the computational algorithm on the characteristics of the process is examined.     

Coulomb oscillations of conductance in an open ring interferometer in a strong magnetic field

Under the conditions corresponding to tunnel-coupled edge current states in an open ring interferometer, oscillations of conductance as a function of gate voltage with two noticeably different periods are observed. The large-period oscillations are attributed to the electron tunneling between the source and drain regions via a closed edge state of the ring, when an integral number of magnetic flux quanta passes through its contour at the Fermi level. The small-period oscillations are explained by the effect of single-electron variations of the ring potential on the transparency of the barriers between the localized and delocalized edge states of the interfer-ometer.     

Spin Josephson current in a ferromagnet/noncentrosymmetric superconductor junction

We investigate the equilibrium spin transport in a ferromagnet/noncentrosymmetric superconductor (FM/NCS) junction where the NCS has a dominant triplet order parameter and helical edge state. Based on the symmetry analysis and numerical calculation, we demonstrate that there is a nonzero spin supercurrent flowing in the junction, which stems from the exchange coupling between the FM magnetization and triplet Cooper-pair spin. It is also found that a transverse spin current other than the helical edge spin current is flowing along the interface of the junction, and its polarization is related to the longitudinal spin supercurrent. Besides, an equilibrium Hall current is also shown to flow along the junction’s interface due to the broken time-reversal symmetry from the FM.     

Synchronization, anti-synchronization and current transports in non-identical chaotic ratchets

The synchronization (CS) and anti-synchronization (AS) of two non-identical inertial ratchets moving in different asymmetric potentials and transporting particles chaotically is demonstrated based on a technique derived from nonlinear control theory. It is shown that in the CS state, particle current is enhanced; while in the AS state, the particles transport current in different directions, suggesting that AS phenomenon could be exploited as a mechanism for particle separation.     

Spectral Structure and Doublon Dissociation in the Two-Particle Non-Hermitian Hubbard Model

Strongly-correlated systems in non-Hermitian models are an emergent area of research. Herein, a non-Hermitian Hubbard model is considered, where the single-particle hopping amplitudes on the lattice are not reciprocal, and provide exact analytical results of the spectral structure in the two-particle sector of Hilbert space under different boundary conditions. The analysis unveils some interesting spectral and dynamical effects of purely non-Hermitian nature and that deviate from the usual scenario found in the single-particle regime. Specifically, a spectral phase transition of the Mott-Hubbard band on the infinite lattice is predicted as the interaction energy is increased above a critical value, from an open to a closed loop in complex energy plane, and the dynamical dissociation of doublons, i.e., instability of two-particle bound states, in the bulk of the lattice, with a sudden revival of the doublon state when the two particles reach the lattice edge. Particle dissociation observed in the bulk of the lattice is a clear manifestation of non-Hermitian dynamics arising from the different lifetimes of single-particle and two-particle states, whereas the sudden revival of the doublon state at the boundaries is a striking burst edge dynamical effect peculiar to non-Hermitian systems with boundary-dependent energy spectra, here predicted for the first time for correlated particles.     

New micromagnetic states of magnetically soft nanoparticles with a nearly cubic shape

The ground state of nonellipsoidal particles can be inhomogeneous due to the effect of a demagnetizing field. The approach proposed here for studying such particles is based on the combination of symmetry analysis and perturbation theory. The general formulation of this approach, which makes it possible to analyze weakly inhomogeneous states for particles with a complex shape, is considered. The ground state of cubic particles of magnetically soft materials is calculated analytically, and the effect of small strains of cubic particles on the magnetization distribution in the particles is investigated. It is shown for the example of magnetically soft cubic particles that even a small deviation of the particle shape from symmetrical may result in the realization of a special magnetic state in such particles, in which the symmetry in the magnetization distribution is lower than the particle symmetry. A change in the parameters of a particle can substantially modify its magnetic properties and may even induce a phase transition to a state with a different symmetry.     

Optically engineering the topological properties of a spin Hall insulator

Time-periodic perturbations can be used to engineer topological properties of matter by altering the Floquet band structure. This is demonstrated for the helical edge state of a spin Hall insulator in the presence of monochromatic circularly polarized light. The inherent spin structure of the edge state is influenced by the Zeeman coupling and not by the orbital effect. The photocurrent (and the magnetization along the edge) develops a finite, helicity-dependent expectation value and turns from dissipationless to dissipative with increasing radiation frequency, signalling a change in the topological properties. The connection with Thouless' charge pumping and nonequilibrium zitterbewegung is discussed, together with possible experiments.     

Deformation and motion by gravity and magnetic field of a droplet of water-based magnetic fluid on a hydrophobic surface

Motion and deformation of a water-based magnetic fluid on a hydrophobic surface were investigated under gravity and a magnetic field. Surface energy and the resultant contact angle of the magnetic fluid depend on the surfactant concentration. The fluid viscosity is governed mainly by magnetite concentration. The front edge of the droplet moved under a weak external field. The rear edge required a higher external field for movement. The forces of gravity and the magnetic field for moving of the front edge are almost equal. However, those of the rear edge are different. The motion of magnetic fluids by an external field depends on concentrations of surfactants and magnetic particles, the external field, and experimental assembly.     

Modeling of Large ELM Suppressions for High Confinement Plasma in D Ⅲ-D

The H-mode discharges with high edge pressure gradients are expected for the economic feasibility of future fusion reactors. However, the high edge pressure gradients easily produce ELM instability , which generally can expel large, heat and particle loading to the divertor targets. These ELMs limit the core plasma performance and reduce the lifetime of divertor target plates. The transports of heat and particles outward across plasma boundary are useful to control density and impurity profiles for achieving steady state, high performance plasmas. Consequently, any technique to eliminate or mitigate large fast ELM impulses must replace the transient heat and particle transports with another slow process. Such a technique is high priority for a burning plasma device such as ITER.     

Positive cross correlations in a normal-conducting fermionic beam splitter

We investigate a beam-splitter experiment implemented in a normal-conducting fermionic electron gas in the quantum Hall regime. The cross correlations between the current fluctuations in the two exit leads of the three terminal device are found to be negative, zero, or even positive, depending on the scattering mechanism within the device. Reversal of the cross correlation sign occurs due to interaction between different edge states and does not reflect the statistics of the fermionic particles which "antibunch."