Time Evolution Of Charge Research Articles

Analysis of a Resistive-Capacitive Shunted Josephson Junction with Topologically Nontrivial Barrier Coupledto a RLC Resonator

This paper presents the resistive-capacitive shunted Josephson junction (RCSJJ) with a topologically nontrivial barrier (TNB) coupled to a linear RLC resonator. The rate equations describing RCSJJ with TNB coupled to the linear RLC resonator are established via Kirchhoff’s current and voltage laws. The model exhibits four, two, or no equilibrium points depending on the external direct current (DC) source and the fractional parameter. The stability analysis of the equilibrium points with credit to the Routh-Hurwitz stability criterion reveals that the stability of equilibrium points depends on the DC source and the fractional parameter. Current-voltage characteristic reveals the presence of a birhythmicity zone which is sensitive to the fractional parameter m. As the fractional parameter increases, the coexistence of the resonant state is destroyed, which is followed simultaneously by the appearance of a new resonance state. Depending on initial conditions, birhythmic behaviour is characterized by the existence of a limit cycle. The projection of the phase space in the specific plane and the time evolution of charge is predicted in which the amplitude of attractors reported is sensitive to the parameter m. Lastly, with a defined fractional parameter, the amplitude of the branch locked to the resonator is greater than the unlocked branch.

Spectral function of Mott-insulating Hubbard ladders: From fractionalized excitations to coherent quasiparticles

We study the spectral function of two-leg Hubbard ladders with the time-dependent density matrix renormalization group method (tDMRG). The high-resolution spectrum displays features of spin-charge separation and a scattering continuum of excitations with coherent bands of bound states `leaking' from it. As the inter-leg hopping is increased, the continuum in the bonding channel moves to higher energies and spinon and holon branches merge into a single coherent quasi-particle band. Simultaneously, the spectrum undergoes a crossover from a regime with two minima at incommensurate values of $k_x$ (a Mott insulator), to one with a single minimum at $k_x=\pi$ (a band insulator). We identify the presence of a continuum of scattering states consisting of a triplon and a polaron. We analyze the processes leading to quasiparticle formation by studying the time evolution of charge and spin degrees of freedom in real space after the hole is created. At short times, incoherent holons and spinons are emitted but after a characteristic time $\tau$ charge and spin form polarons that propagate coherently.

Difference in charge and spin dynamics in a quantum dot–lead coupled system

We analyze time evolution of charge and spin states in a quantum dot coupled to an electric reservoir. Utilizing high-speed single-electron detection, we focus on dynamics induced by the first-order tunneling. We find that there is a difference between the spin and the charge relaxation: the former appears slower than the latter. The difference depends on the Fermi occupation factor and the spin relaxation becomes slower when the energy level of the quantum dot is lowered. We explain this behavior by a theory which includes the first-order tunneling processes. We conduct detailed comparison of the experiment and the theory with changing the energy of the quantum dot levels, and the theory can reproduce the experimental results.

Josephson junction in the quantum mesoscopic electric circuits with charge discreteness

A quantum mesoscopic electrical LC-circuit with charge discreteness including a Josephson junction is considered and a nonlinear Hamiltonian that describing the dynamic of such circuit is introduced. The quantum dynamical behavior (persistent current probability) is studied in the charge and phase regimes by numerical solution approaches. The time evolution of charge and current, number-difference and the bosonic phase and also the energy spectrum of a quantum mesoscopic electric LC-circuit with charge discreteness that coupled with a Josephson junction device are investigated. We show the role of the coupling energy and the electrostatic Coulomb energy of the Josephson junction in description of the quantum behavior and the spectral properties of a quantum mesoscopic electrical LC-circuits with charge discreteness.

Higher-order spin and charge dynamics in a quantum dot-lead hybrid system

Understanding the dynamics of open quantum systems is important and challenging in basic physics and applications for quantum devices and quantum computing. Semiconductor quantum dots offer a good platform to explore the physics of open quantum systems because we can tune parameters including the coupling to the environment or leads. Here, we apply the fast single-shot measurement techniques from spin qubit experiments to explore the spin and charge dynamics due to tunnel coupling to a lead in a quantum dot-lead hybrid system. We experimentally observe both spin and charge time evolution via first- and second-order tunneling processes, and reveal the dynamics of the spin-flip through the intermediate state. These results enable and stimulate the exploration of spin dynamics in dot-lead hybrid systems, and may offer useful resources for spin manipulation and simulation of open quantum systems.

Diagnostics of many-particle electronic states: Non-stationary currents and residual charge dynamics

We propose the method for identifying many particle electronic states in the system of coupled quantum dots (impurities) with Coulomb correlations. We demonstrate that different electronic states can be distinguished by the complex analysis of localized charge dynamics and non-stationary characteristics. We show that localized charge time evolution strongly depends on the properties of initial state and analyze different time scales in charge kinetics for initially prepared singlet and triplet states. We reveal the conditions for existence of charge trapping effects governed by the selection rules for electron transitions between the states with different occupation numbers.

Correlation between transient evolutions of the gate and drain currents in AlGaN/GaN technologies

This work focuses on short term and long term time evolution of charges in the context of early identification of failure mechanisms in AlGaN/GaN High Electron Mobility Transistors (HEMTs). High power and high frequency devices are needed for new microwave applications, and large band-gap HEMTs offer a powerful alternative to traditional technologies (Si, GaAs, SiGe etc.); however, reliability issues still hamper the potential of these technologies to push their limits in terms of mean time to failure or junction temperature. This paper contributes to the investigation of transient behaviors of gate and drain currents over a large time scale for gallium nitride HEMTs; a correlation is found between the currents' evolution, in spite of the non-monotonic behavior, and a model is given through a mathematical relationship. Charges under the gated zone of the transistor are found to evolve with time, and turn into command variations of the electron density in the 2DEG. This work addresses the consequences of charge dependent mechanisms on the drain current's drop, and thus of the output power.

Coulomb correlations effects on localized charge relaxation in the coupled quantum dots

We analyzed localized charge time evolution in the system of two interacting quantum dots (QD) (artificial molecule) coupled with the continuous spectrum states. We demonstrated that Coulomb interaction modifies relaxation rates and is responsible for non-monotonic time evolution of the localized charge. We suggested new mechanism of this non-monotonic charge time evolution connected with charge redistribution between different relaxation channels in each QD.

Relevant parameters involved in tribocharging of powders during dilute phase pneumatic transport

This work presents the results of an experimental study carried out on the tribo-charging of fine glass particles during their pneumatic conveying. The effect of several parameters such as the chemical nature of the transport pipe, the particles mean size, the solids flow rate, the air velocity and the relative humidity (RH) was examined. Experiments were carried out using several batches of monodisperse glass particles with mean particle sizes ranging from 75 μm to 500 μm. Both spherical and angular particles were used. Powders were conveyed through two types of pipe materials (Teflon and Nylon) at dilute loadings and varying relative humidities of air (0–90%). The total charge of conveyed powder was measured using a terminal Faraday cage. Furthermore, a series of four Faraday cages was used to measure the charge transfer between the wall and particles along the flow path. Greater electrostatic effects were observed for larger particles, higher air velocities, higher solids flowrate and lower RH. A simple model of charge transfer was also established in order to describe the time evolution of charges on the particles and the wall. Results showed that the tribocharging rate can be conveniently represented by an exponential-deceleration model.

Charge, Lattice, and Spin Dynamics in Photoinduced Phase Transitions from Charge-Ordered Insulator to Metal in Quasi-Two-Dimensional Organic Conductors

To elucidate different photoinduced melting dynamics of charge orders observed in quasi-two-dimensional organic conductors $ \theta $-(BEDT-TTF)$_2$RbZn(SCN)$_4$ and $ \alpha $-(BEDT-TTF)$_2$I$_3$ [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene], we theoretically study photoinduced time evolution of charge and spin correlation functions on the basis of exact many-electron wave functions coupled with classical phonons in extended Peierls-Hubbard models on anisotropic triangular lattices. In both salts, the so-called horizontal-stripe charge order is stabilized by nearest-neighbor repulsive interactions and by electron-lattice interactions. In $ \theta $-(BEDT-TTF)$_2$RbZn(SCN)$_4$ (abbreviated as $ \theta $-RbZn), the stabilization energy due to lattice distortion is larger, so that larger quantity of energy needs to be absorbed for the melting of the charge and lattice orders. The photoinduced charge dynamics shows a complex behavior owing to a substantial number of nearly degenerate eigenstates involved. This is related to the high structural symmetry when the lattice is undistorted. In $ \alpha $-(BEDT-TTF)$_2$I$_3$ (abbreviated as $ \alpha $-I$_3$), the lattice stabilization energy is smaller, and smaller quantity of energy is sufficient to melt the charge and lattice orders leading to a metallic phase. The photoinduced charge dynamics shows a sinusoidal oscillation. In $ \alpha $-I$_3$, the low structural symmetry ensures nearly spin-singlet bonds between hole-rich sites, where the spin correlation survives even after photoexcitation.

The insulation structure of the 1 MV transmission line for the ITER neutral beam injector

The paper describes the studies and the tests for the development of the insulation structure of the 1 MV–50 A gas insulated (SF 6) line of the ITER NBI in the SinGap configuration characterized by two kinds of spacers: at least a couple of disk-shaped spacers, designed to be gas tight, and a larger number (several tens) of inner conductor post spacers. To this aim a test campaign has been carried out to assess the capability of standard epoxy spacers to withstand a high dc voltage with frequent short circuits, simulating the operational condition for the ITER NBI. Two computational tools, the first for the epoxy spacer shape optimization under electrostatic distribution and the other for the nonlinear time variant evolution of the electric field and surface charge, have been developed specifically for designing epoxy spacer under dc voltage stress. The results on the optimization of the disk spacer and on the electric field–surface charge time evolution of the post spacer are reported and discussed. The effects of the SF 6 radiation induced conductivity on the post spacer are also reported.

The time evolution of charge and current in mesoscopic LC circuit with charge discreteness

This Letter mainly investigates dynamic behavior of charge and current in a mesoscopic LC circuit with charge discreteness by considering coupling energy of the mesoscopic capacitor. The results indicate that the time evolution function of charge or current is the Jacobi elliptic function instead of a sine one, and the squeezing effect appears periodically in the circuit.

Quantitative Charge Imaging of Silicon Nanocrystals by Atomic Force Microscopy

ABSTRACTQuantitative understanding of charging and discharging of Si nanocrystals in SiO2 films on Si substrate is essential to their application in floating gate nonvolatile memory devices. Charge imaging by atomic force microscopy (AFM) or electrostatic force microscopy (EFM) can provide qualitative information on such system, while a further step is needed. We have developed a generalized method of images, which can solve Poisson equation for multiple dielectric layers, to simulate the charge imaging of Si nanocrystals by non-contact mode AFM under different sample geometries. Simulated images can be compared with experimental images thoroughly to estimate the total amount and distributions of trapped charges, which is also useful in the study of time evolution of charges or dissipation problems.

Quantum noise reduction of electrical circuit having a time-dependent parameter: transient behaviour and damping

In a previous paper [Physica A 197 (1993) 364] it was shown that a quantized, time-dependent LC-circuit, is able to generate squeezing effect, its amount being controlled by the final value of the inductance. In the present work we pursue further this topic studying the transient regime and its influence upon the squeezing effect. A damping in the time evolution of charge and current in the circuit is found, in spite of having no dissipative element in the system.

Study of amorphous silicon high voltage transistors using novel electron microscopy techniques

Variants of scanning electron microscopy techniques developed by the authors allow detailed studies to be performed of the operation of thin-film active semiconductor devices. In particular, using a synchronised gating procedure, we are able to obtain time-resolved measurements of the spatial distribution of electrical charge throughout the operational cycle of the high voltage thin film transistors (HVTFTs) developed by Tuan and colleagues at Xerox's Palo Alto Research Centre. These devices operate in a space-charge limited mode. Consequently, the time evolution of charge within the channel, the residual trapped charge, etc. are of critical importance. Hack and co-workers at Xerox have generated computer simulations of such characteristics, but we believe that the present programme represents the first direct experimental investigation. In this paper, we outline the experimental technique and present some of the initial results of the study.