Aharonov-Casher phase and persistent current in a polyacetylene ring

We investigate a polyacetylene ring in an axially symmetric, static electric field with a modified SSH Hamiltonian of a polyacetylene chain. An effective gauge potential of the single electron Hamiltonian due to spin-field interaction is obtained and it results in a Fr\"{o}hlich's type of superconductivity equivalent to the effect of travelling lattice wave. The total energy as well as the persistent current density are shown to be a periodic function of the flux of the gauge field embraced by the polyacetylene ring.Comment: 12 pages, 5 figure

Fermionic R-operator approach for the small-polaron model with open boundary condition

Exact integrability and algebraic Bethe ansatz of the small-polaron model with the open boundary condition are discussed in the framework of the quantum inverse scattering method (QISM). We employ a new approach where the fermionic R-operator which consists of fermion operators is a key object. It satisfies the Yang-Baxter equation and the reflection equation with its corresponding K-operator. Two kinds of 'super-transposition' for the fermion operators are defined and the dual reflection equation is obtained. These equations prove the integrability and the Bethe ansatz equation which agrees with the one obtained from the graded Yang-Baxter equation and the graded reflection equations.Comment: 10 page

The Influence of Molecular Adsorption on Elongating Gold Nanowires

Using molecular dynamics simulations, we study the impact of physisorbing adsorbates on the structural and mechanical evolution of gold nanowires (AuNWs) undergoing elongation. We used various adsorbate models in our simulations, with each model giving rise to a different surface coverage and mobility of the adsorbed phase. We find that the local structure and mobility of the adsorbed phase remains relatively uniform across all segments of an elongating AuNW, except for the thinning region of the wire where the high mobility of Au atoms disrupts the monolayer structure, giving rise to higher solvent mobility. We analyzed the AuNW trajectories by measuring the ductile elongation of the wires and detecting the presence of characteristic structural motifs that appeared during elongation. Our findings indicate that adsorbates facilitate the formation of high-energy structural motifs and lead to significantly higher ductile elongations. In particular, our simulations result in a large number of monatomic chains and helical structures possessing mechanical stability in excess of what we observe in vacuum. Conversely, we find that a molecular species that interacts weakly (i.e., does not adsorb) with AuNWs worsens the mechanical stability of monatomic chains.Comment: To appear in Journal of Physical Chemistry

Quantum Phase Interference for Quantum Tunneling in Spin Systems

The point-particle-like Hamiltonian of a biaxial spin particle with external magnetic field along the hard axis is obtained in terms of the potential field description of spin systems with exact spin-coordinate correspondence. The Zeeman energy term turns out to be an effective gauge potential which leads to a nonintegrable pha se of the Euclidean Feynman propagator. The phase interference between clockwise and anticlockwise under barrier propagations is recognized explicitly as the Aharonov-Bohm effect. An additional phase which is significant for quantum phase interference is discovered with the quantum theory of spin systems besides the known phase obtained with the semiclassical treatment of spin. We also show the energ y dependence of the effect and obtain the tunneling splitting at excited states with the help of periodic instantons.Comment: 19 pages, no figure, to appear in PR

Tunnel splitting and quantum phase interference in biaxial ferrimagnetic particles at excited states

The tunneling splitting in biaxial ferrimagnetic particles at excited states with an explicit calculation of the prefactor of exponent is obtained in terms of periodic instantons which are responsible for tunneling at excited states and is shown as a function of magnetic field applied along an arbitrary direction in the plane of hard and medium axes. Using complex time path-integral we demonstrate the oscillation of tunnel splitting with respect to the magnitude and the direction of the magnetic field due to the quantum phase interference of two tunneling paths of opposite windings . The oscillation is gradually smeared and in the end the tunnel splitting monotonously increases with the magnitude of the magnetic field when the direction of the magnetic field tends to the medium axis. The oscillation behavior is similar to the recent experimental observation with Fe$_8$ molecular clusters. A candidate of possible experiments to observe the effect of quantum phase interference in the ferrimagnetic particles is proposed.Comment: 15 pages, 5 figures, acceptted to be pubblished in Physical Review

Energetic ion injection and formation of the storm-time symmetric ring current

An extensive study of ring current injection and intensification of the storm-time ring current is conducted with three-dimensional (3-D) test particle trajectory calculations (TPTCs). The TPTCs reveal more accurately the process of ring current injection, with the main results being the following: (1) an intense convection electric field can effectively energize and inject plasma sheet particles into the ring current region within 1–3 h. (2) Injected ions often follow chaotic trajectories in non-adiabatic regions, which may have implications in storm and ring current physics. (3) The shielding electric field, which arises as a consequence of enhanced convection and co-exists with the injection and convection electric field, may cause the original open trajectories of injected ions with higher energy to change into closed ones, thus playing a role in the formation of the symmetric ring current

Three‐dimensional lunar wake reconstructed from ARTEMIS data

Data from the two‐spacecraft Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun mission to the Moon have been exploited to characterize the lunar wake with unprecedented fidelity. The differences between measurements made by a spacecraft in the solar wind very near the Moon and concurrent measurements made by a second spacecraft in the near lunar wake are small but systematic. They enabled us to establish the perturbations of plasma density, temperature, thermal, magnetic and total pressure, field, and flow downstream of the Moon to distances of 12 lunar radii ( R M ). The wake disturbances are initiated immediately behind the Moon by the diamagnetic currents at the lunar terminator. Rarefaction waves propagate outward at fast MHD wave velocities. Beyond ~6.5 R M , all plasma and field parameters are poorly structured which suggests the presence of instabilities excited by counter‐streaming particles. Inward flowing plasma accelerated through pressure gradient force and ambipolar electric field compresses the magnetic field and leads to continuous increase in magnitude of magnetic perturbations. Besides the downstream distance, the field perturbation magnitude is also a function of the solar wind ion beta and the angle between the solar wind and the interplanetary magnetic field (IMF). Both ion and electron temperatures increase as a consequence of an energy dispersion effect, whose explanation requires fully kinetic models. Downstream of the Moon, the IMF field lines are observed to bulge toward the Moon, which is unexpected and may be caused by a plasma pressure gradient force or/and the pickup of heavy charged dust grains behind the Moon. Key Points The 3‐D lunar wake is studied with well‐determined solar wind conditions The field lines bend in the wake due to flow deceleration The 3‐D wake structure is investigated by observation dataPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108259/1/jgra51135.pd

Enhancement of Quantum Tunneling for Excited States in Ferromagnetic Particles

A formula suitable for a quantitative evaluation of the tunneling effect in a ferromagnetic particle is derived with the help of the instanton method. The tunneling between n-th degenerate states of neighboring wells is dominated by a periodic pseudoparticle configuration. The low-lying level-splitting previously obtained with the LSZ method in field theory in which the tunneling is viewed as the transition of n bosons induced by the usual (vacuum) instanton is recovered. The observation made with our new result is that the tunneling effect increases at excited states. The results should be useful in analyzing results of experimental tests of macroscopic quantum coherence in ferromagnetic particles.Comment: 18 pages, LaTex, 1 figur