Showing papers on "Finite potential well published in 1994"

Three-body halos: Gross properties.

Abstract: Three-body bound systems are investigated in the limit of very weak binding by use of hyperspherical harmonics. The short-range two-body potentials are assumed to be unable to bind the binary subsystems. Then the mean square radius always converges for vanishing binding except for the most spherical wave function, where all angular momenta involved are zero, which diverges logarithmically. Universal scaling properties are suggested. Any additional long-range repulsive potential, like, for example, the Coulomb potential, leads to finite radial moments even for vanishing binding. Spatially extended charged halos are only possible for very low charges. The spatial extension of three-body systems is in the asymptotic region more confined than for corresponding two-body systems, where the divergences are stronger and more abundant. Numerical examples and transitions to the asymptotic region are shown for square well and Gaussian two-body potentials. The results are applied to several drip-line nuclei.

Resonant tunnelling of a composite particle through a single potential barrier

Abstract: Some aspects of quantum tunnelling of a composite particle are clarified by a simple model. We calculate the probability that a couple of point particles bound to each other by a square well potential with a hard core tunnel through a rectangular potential barrier. It is shown that resonance structures appear in the transmission spectrum in some cases, which reflects the existence of quasi-bound-states of the centre of mass motion around the potential barrier. It is also shown that an inelastic tunnelling occurs in which the transitions in the relative motion are induced by the tunnelling of the centre of mass.

Efficient evaluation of three-phase coexistence lines

Abstract: The Gibbs-Duhem integration method is a means for evaluating phase diagrams by molecular simulation. Starting from a state of known phase coexistence, one applies the Clapeyron equation to trace out subsequent points on the saturation line. Each simulation yields a coexistence state, and particle exchanges are not invoked to insure equality of fugacities. We describe and demonstrate here the extension of this method to three-phase coexistence, namely, among a solid, a liquid, and a gas. In one application, we compute the saturation pressure and temperature as a function of composition (more accurately, as a function of fugacity fraction) for six Lennard-Jones two-component mixtures. In a second study, we traverse a mutation pathway; that is, we evaluate three-phase equilibriaas a function of the intermolecular potential. In particular, we define a path that transforms the Lennard-Jones model into a square well, and thus in our calculations we quantify the effect of the shape of the repulsive and attractive portions of the potential on the triple point. In the end we have what is, to our knowledge, the First estimate of a state of solid-fluid coexistence for a square well model. In both applications we assume that the fee crystal structure represents the thermodynamically stable solid phase.

Dynamical behavior and energy dissipation of a classical particle in harmonic-plus-Legendre potential.

Abstract: The dynamical motion of a classical particle in a potential taken as the sum of harmonic oscillator and time-independent or time-dependent multipolar Legendre function was investigated. Starting from various initial conditions, with increasing strength of the Legendre potential, which broke down the rotational invariance of the system, the dynamical behavior of the particle changed from regular to chaotic type. Meanwhile the local curvature of the potential surface may change from positive to zero, and negative sign. This negative curvature was demonstrated to be responsible for the local instability of a trajectory. Only via the mechanism of chaotic particle motion could the time-dependent potential permanently exchange energy with the particle. Contrasting this phenomenon with properties of independent particle model of nucleus with spherical or deformed shape would shed light on the foundation of significant property of the corresponding quantum system and the mechanism of the energy dissipation during nuclear reaction process.

Tunnelling spectroscopy of 0D states

Abstract: We have studied tunnelling processes between a multiple quantum dot (MQD) system and a two-dimensional electron gas (2DEG) system, which are realized on a GaAs-AlGaAs-GaAs heterostructure. Using a transfer Hamiltonian formalism. It is shown that the tunnelling probability for transitions between a zero-dimensional (0D) and a two-dimensional (2D) state strongly depends on the quantum dot potential profile. In the case of a square well potential, only the resonance of the ground state is pronounced significantly, whereas for a cosine-shaped quantum dot potential profile a multitude of resonance structures is caused by each 0D state. From our experimental results we conclude that the potential of the quantum dots is best described by a cosine-shaped profile. In addition, the subband spacings and the extent of the wavefunctions of the individual subbands are also determined directly.

Confinement and infinite potential

Abstract: We discuss the confinement problem with infinite vector and scalar potentials. Infinite potentials like harmonic oscillator potential and linear one are investigated. We show the particle cannot be confined when the vector potential is larger than the scalar one. It is also shown the existence of a bound state in 3-dimensional square well potentials, but this does not mean confinement of the particle.

Detection of particles under a potential barrier

Abstract: We introduce a model detector which registers the passage of a particle through the detector location, without substantially perturbing the particle wave function. (The exact time of passage is not determined in such measurements.) We then show that our detector can operate in a classically forbidden reigon and register particles passing through a certain point under a potential barrier. We show that it should be possible to observe the particle's track under the barrier.

Electrostatic correction to the square-potential model of nanostructures significantly affects current resonances

Abstract: Depletion of carriers in nanostructures generates an electrostatic correction to the square potential model. This correction changes the tunneling probability and consequently affects current resonances. We analyze this effect numerically for the double-barrier quantum well (DBQW) at various temperatures and carrier densities, and conclude that the electrostatic correction significantly affects the resonant voltage, the current at resonance, the peak-to-valley ratio, and may even cause disappearance of the lowest resonance.