2,588 research outputs found
Resonant quantum coherence of magnetization at excited states in nanospin systems with different crystal symmetries
The quantum interference effects induced by the Wess-Zumino term, or Berry
phase are studied theoretically in resonant quantum coherence of magnetization
vector between degenerate excited states in nanometer-scale single-domain
ferromagnets in the absence of an external magnetic field. By applying the
periodic instanton method in the spin-coherent-state path integral, we evaluate
the low-lying tunnel splittings between degenerate excited states of
neighboring wells. And the low-lying energy level spectrum of m-th excited
states are obtained with the help of the Bloch theorem in one-dimensional
periodic potential.Comment: 23 pages, final version and accepted by Eur. Phys. J.
Non-equilibrium dynamics of simple spherical spin models
We investigate the non-equilibrium dynamics of spherical spin models with
two-spin interactions. For the exactly solvable models of the d-dimensional
spherical ferromagnet and the spherical Sherrington-Kirkpatrick model the
asymptotic dynamics has for large times and for large waiting times the same
formal structure. In the limit of large waiting times we find in both models an
intermediate time scale, scaling as a power of the waiting time with an
exponent smaller than one, and thus separating the time-translation invariant
short-time dynamics from the aging regime. It is this time scale on which the
fluctuation-dissipation regime is violated. Aging in these models is similar to
that observed in spin glasses at the level of correlation functions, but
different at the level of response functions, and thus different at the level
of experimentally accessible quantities like the thermoremanent magnetization.Comment: 8 pages, 1 eps figur
One Explanation for the Exotic State Y(4260)
In this Letter we interpret the Y(4260), a state recently discovered by the
BaBar Collaboration that has a mass within the range of conventional charmonium
states, as having a molecular-state structure. In our scheme this
molecular-like state is not constructed out of two-quark mesons, but rather out
of baryons, i.e., the Y(4260) is a baryonium state. With this interpretation,
the unusual measured properties of the Y(4260) are easily understood and some
further peculiar decay characteristics are predicted.Comment: five text pages, one ps figure. Version to appear in PL
Numerical approximation of a phase-field surfactant model with fluid flow
Modelling interfacial dynamics with soluble surfactants in a multiphase
system is a challenging task. Here, we consider the numerical approximation of
a phase-field surfactant model with fluid flow. The nonlinearly coupled model
consists of two Cahn-Hilliard-type equations and incompressible Navier-Stokes
equation. With the introduction of two auxiliary variables, the governing
system is transformed into an equivalent form, which allows the nonlinear
potentials to be treated efficiently and semi-explicitly. By certain subtle
explicit-implicit treatments to stress and convective terms, we construct first
and second-order time marching schemes, which are extremely efficient and
easy-to-implement, for the transformed governing system. At each time step, the
schemes involve solving only a sequence of linear elliptic equations, and
computations of phase-field variables, velocity and pressure are fully
decoupled. We further establish a rigorous proof of unconditional energy
stability for the first-order scheme. Numerical results in both two and three
dimensions are obtained, which demonstrate that the proposed schemes are
accurate, efficient and unconditionally energy stable. Using our schemes, we
investigate the effect of surfactants on droplet deformation and collision
under a shear flow, where the increase of surfactant concentration can enhance
droplet deformation and inhibit droplet coalescence
- …