Presence Of Perpendicular Electric Field Research Articles

Impact of hot injected beam on whistler mode with alternating electric field (AC) in the magnetosphere of Saturn

Whistlers are believed to be generated by its own and responsible to evolve dynamical properties of magnetized planetary environment. Growing whistler instability can cause other uncertainties in the magnetosphere and evident to be generated by mean of injection events and temperature variance in plasma environment. In this paper the empirical dispersion relation has developed for parallel propagating whistler mode instability in an infinite saturnian magneto plasma in the presence of perpendicular electric field for ring distribution function having non-monotonous nature. Method of characteristics solutions alongside kinetic approach found to be most suitable in order to achieve perturbed plasma states. The perturbed and unperturbed particle trajectories have taken into consideration to determine perturbed distribution function. A remarkable growth rate expression with added hot plasma injection has been calculated in inner magnetosphere near 6.18 Rs. The results obtained using demonstrative value of the parameters suited to the Saturnian magnetosphere have been computed and discussed. Pressure (Temperature) anisotropy is found to be a peculiar source of free energy for whistler mode instability. The AC frequency irrespective of its magnitude, affects the growth rate significantly. The bulk of energetic hot electrons injection influences the growth rate by increasing its peak value. The result obtained provide the important view of wave particle interaction and useful to analyze the VLF emissions observed over a wide frequency range.

Exciton Vortices in Two-Dimensional Hybrid Perovskite Monolayers* *Supported by the National Key R&D Programme of China (Grant Nos. 2017YFA0303400 and 2016YFE0110000), the National Natural Science Foundation of China (Grant Nos. 11574303 and 11504366), the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 2018148), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000).

We study theoretically the exciton Bose–Einstein condensation and exciton vortices in a two-dimensional (2D) perovskite (PEA)2PbI4 monolayer. Combining the first-principles calculations and the Keldysh model, the exciton binding energy of in a (PEA)2PbI4 monolayer can approach hundreds of meV, which make it possible to observe the excitonic effect at room temperature. Due to the large exciton binding energy, and hence the high density of excitons, we find that the critical temperature of the exciton condensation could approach the liquid nitrogen regime. In the presence of perpendicular electric fields, the dipole-dipole interaction between excitons is found to drive the condensed excitons confined in (PEA)2PbI4 monolayer flakes into patterned vortices, as the evolution time of vortex patterns is comparable to the exciton lifetime.

Magnetic properties of β12-borophene in the presence of electric field and dilute charged impurity

Abstract Monoatomic lattice of boron atoms (borophene), a new low-dimensional material shows promising physical and chemical properties. Recently, on the most stable borophene, metal β 12 -borophene, electronic phase transition from metal-to-semimetal and metal-to-semiconductor in the presence of perpendicular electric field and dilute charged impurity is found, respectively. From this point, in this paper, we study the magnetic properties of the electric field and charged impurity induced β 12 -borophene. Particularly, we have calculated Pauli spin paramagnetic susceptibility (PSPS) quantity using the five-band tight-binding Hamiltonian and the Green’s function approach for different interaction-dependent models. The charged impurity and perpendicular electric field effects on the susceptibility of β 12 -borophene show that the “pristine” PSPS of inversion symmetric model in β 12 -borophene is larger than the homogeneous model as well as the Dirac fermions contribute to the total PSPS more than triplet fermions. Further, we found out that the dilute charged impurity does not influence PSPS of the principle system significantly at all temperatures and it decreases slightly with impurity concentration and scattering potential. On the other hand, electric field-induced PSPS results in an increasing (decreasing) trend for PSPS at very low (intermediate and high) temperatures. Our findings pave the way for the industrial practical applications.

On the influence of dilute charged impurity and perpendicular electric field on the electronic phase of phosphorene: Band gap engineering

Tuning the band gap plays an important role for applicability of 2D materials in the semiconductor industry. The present paper is a theoretical study on the band gap engineering using the electronic density of states (DOS) of phosphorene in the presence of dilute charged impurity and of a perpendicular electric field. The electronic DOS is numerically calculated using a combination of the continuum model Hamiltonian and the Green's function approach. Our findings show that the band gap of phosphorene in the absence and presence of the perpendicular electric field decreases with increasing impurity concentration and/or impurity scattering potential. Further, we found that in the presence of opposite perpendicular electric fields, the electronic DOS of disordered phosphorene shows different changing behaviors stemming from the Stark effect: in the positive case the band gap increases with increasing electric-field strength; whereas in the negative case the band gap disappears. The latter, in turn, leads to the semiconductor-to-semimetal and semiconductor-to-metal phase transition for the case of strong impurity concentrations and strong impurity scattering potentials, respectively. The results can serve as a base for future applications in logic electronic devices.

Tunable band gap, magnetoresistance and pseudo-magnetoresistance in silicene-based nanodevices

Spin-dependent transport in two terminal zigzag silicene nanoribbon is investigated numerically in the presence of spin-orbit interactions, external spin splittings or exchange fields, and perpendicular electric field. We show by applying an exchange field, a tunable band gap emerges which depends on the exchange field vector angle with the plane of nanoribbon. Such behavior is interpreted using the low-energy Hamiltonian of the silicene which indicates qualitative agreement with results obtained from lattice model. Moreover, it is found that by decreasing the width of nanoribbon larger band gaps are achievable which can be promising for nanoelectronic applications. On the other hand, by imposing exchange fields inside the electrodes, the magnetoresistance of the junction is investigated. As a main result we observe that when the Rashba interaction becomes stronger the magnetoresistance decreases but it is not fully suppressed. Finally, in the presence of perpendicular electric fields applied to the electrodes, depending on their relative configuration, the so-called pseudomagnetoresistance is calculated. Our results indicates that the conductance of the silicene nanoribbon significantly differs between the parallel and anti-parallel configurations of electric fields in the electrodes.

Controllable spin polarization and spin filtering in a zigzag silicene nanoribbon

Using non-equilibrium Green's function, we study the spin-dependent electron transport properties in a zigzag silicene nanoribbon. To produce and control spin polarization, it is assumed that two ferromagnetic strips are deposited on the both edges of the silicene nanoribbon and an electric field is perpendicularly applied to the nanoribbon plane. The spin polarization is studied for both parallel and anti-parallel configurations of exchange magnetic fields induced by the ferromagnetic strips. We find that complete spin polarization can take place in the presence of perpendicular electric field for anti-parallel configuration and the nanoribbon can work as a perfect spin filter. The spin direction of transmitted electrons can be easily changed from up to down and vice versa by reversing the electric field direction. For parallel configuration, perfect spin filtering can occur even in the absence of electric field. In this case, the spin direction can be changed by changing the electron energy. Finally, we investigate the effects of nonmagnetic Anderson disorder on spin dependent conductance and find that the perfect spin filtering properties of nanoribbon are destroyed by strong disorder, but the nanoribbon retains these properties in the presence of weak disorder.

Antiferromagnetic topological superconductor and electrically controllable Majorana fermions.

We investigate the realization of a topological superconductor in a generic bucked honeycomb system equipped with four types of mass-generating terms, where the superconductor gap is introduced by attaching the honeycomb system to an s-wave superconductor. Constructing the topological phase diagram, we show that Majorana modes are formed in the phase boundary. In particular, we analyze the honeycomb system with antiferromagnetic order in the presence of perpendicular electric field E(z). It becomes topological for |E(z)|>E(z)(cr) and trivial for |E(z)|<E(z)(cr), with E(z)(cr) a certain critical field. It is possible to create a topological spot in a trivial superconductor by controlling applied electric field. One Majorana zero-energy bound state appears at the phase boundary. We can arbitrarily control the position of the Majorana fermion by moving the spot of applied electric field, which will be made possible by a scanning tunneling microscope probe.

Linear theory for fast collisionless magnetic reconnection in the lower-hybrid frequency range

A linear theory is presented for the interplay between the fast collisionless magnetic reconnection and the lower-hybrid waves that has been observed in recent computer simulations [J. F. Drake, M. Swisdak, C. Cattell et al., Science 299, 873 (2003)]. In plasma configurations with a strong guide field and anisotropic electron temperature, the electron dynamics is described within the framework of standard electron magnetohydrodynamic equations, accounting also for the effects of the electron polarization and ion motions in the presence of perpendicular electric fields. In the linear phase, we find two types of instabilities of a thin current sheet with steep edges, corresponding to its filamentation (or tearing) and bending. Using a surface-wave formalism for the perturbations whose wavelength is larger than the thickness of the current sheet, the corresponding growth rates are calculated as the contributions of singularities in the plasma dispersion function. These are governed by the electron inertia and the linear coupling of the reconnecting magnetic field with local plasma modes propagating in the perpendicular direction that are subject to the Buneman instability. The linear surface wave instability may be particularly important as a secondary instability, dissipating the thin current sheets that develop in the course of the fast reconnection in the shear-Alfvén and kinetic-Alfvén regimes, and providing the anomalous resistivity for the growth of magnetic islands beyond the shear-Alfvén and kinetic-Alfvén scales.

Filamentation Instability of Thin Current Sheets in Low-β Plasmas

An analytic theory is presented for the collisionless filamentation instability of thin current sheets in the frequency domain of lower-hybrid waves in low-β plasmas. In a configuration with a strong guide field, the plasma dynamics is studied in a fluid description, accounting for the effects of electron polarization and finite Larmor radii, as well as of the motion of unmagnetized ions in the presence of perpendicular electric fields. In the linear phase, two types of unstable perturbations of a thin current sheet with steep edges are identified that correspond to its filamentation or tearing and bending. Using a surface-wave formalism for the modes whose wavelength is larger than the current sheet thickness, the corresponding growth rates are calculated as the contributions of singularities in the dispersion function of surface waves. These are governed by the electron inertia and by linear coupling with local plasma modes propagating in the perpendicular direction that are subjected to the Buneman instability. This new linear instability provides a suitable channel for the dissipation of current sheets that evolve during the collisionless magnetic reconnection in shear- and kinetic-Alfvén regimes, and for the creation of anomaluos resistivity.

Ordering mechanisms in confined diblock copolymers

We present several ordering mechanisms in diblock copolymers. For temperatures above the order-disorder temperature and in the weak segregation regime, a linear response theory is presented which gives the polymer density in the vicinity of confining flat surfaces. The surfaces are chemically patterned where different regions attract different parts of the copolymer chain. The surface pattern or template is decomposed into its Fourier modes, and the decay of these modes is analyzed. The propagation of the surface pattern into the disordered bulk is given for several types of patterns (e.g. uniform and striped surface). It is further shown that complex morphology can be induced in a thin film even though the bulk is disordered. We next consider lamellar diblock copolymers (low temperature regime) in the presence of a striped surface. It is shown that lamellae acquire a tilt with respect to the surface, if the surface periodicity is larger than the bulk one. The lamellae close to the surface are strongly distorted from their perfect shape. When the surface and lamellar periodicities are equal, the lamellae are perpendicular to the surface. Lastly, the transition from parallel to perpendicular lamellae in a thin film is presented. The transition between the two states depends on the surface separation and strength of surface interactions. We further calculate the phase diagram in the presence of perpendicular electric field favoring perpendicular ordering. In the strong segregation limit we introduce a simple model to calculate the phase diagram of the fully parallel, fully perpendicular and mixed (parallel and perpendicular) states.