24,070 research outputs found
Collective Diffusion and a Random Energy Landscape
Starting from a master equation in a quantum Hamiltonian form and a coupling
to a heat bath we derive an evolution equation for a collective hopping process
under the influence of a stochastic energy landscape. There results different
equations in case of an arbitrary occupation number per lattice site or in a
system under exclusion. Based on scaling arguments it will be demonstrated that
both systems belong below the critical dimension to the same universality
class leading to anomalous diffusion in the long time limit. The dynamical
exponent can be calculated by an expansion. Above the
critical dimension we discuss the differences in the diffusion constant for
sufficient high temperatures. For a random potential we find a higher mobility
for systems with exclusion.Comment: 15 pages, no figure
Kinetic induced phase transition
An Ising model with local Glauber dynamics is studied under the influence of
additional kinetic restrictions for the spin-flip rates depending on the
orientation of neighboring spins. Even when the static interaction between the
spins is completely eliminated and only an external field is taken into account
the system offers a phase transition at a finite value of the applied field.
The transition is realized due to a competition between the activation
processes driven by the field and the dynamical rules for the spin-flips. The
result is based on a master equation approach in a quantum formulation.Comment: 13 page
Universal behavior of the IMS domain formation in superconducting niobium
In the intermediate mixed state (IMS) of type-II/1 superconductors, vortex
lattice (VL) and Meissner state domains coexist due to a partially attractive
vortex interaction. Using a neutron-based multiscale approach combined with
magnetization measurements, we study the continuous decomposition of a
homogeneous VL into increasingly dense domains in the IMS in bulk niobium
samples of varying purity. We find a universal temperature dependence of the
vortex spacing, closely related to the London penetration depth and independent
of the external magnetic field. The rearrangement of vortices occurs even in
the presence of a flux freezing transition, i.e. pronounced pinning, indicating
a breakdown of pinning at the onset of the vortex attraction
Freezing of Spinodal Decompostion by Irreversible Chemical Growth Reaction
We present a description of the freezing of spinodal decomposition in
systems, which contain simultaneous irreversible chemical reactions, in the
hydrodynamic limit approximation. From own results we conclude, that the
chemical reaction leads to an onset of spinodal decomposition also in the case
of an initial system which is completely miscible and can lead to an extreme
retardation of the dynamics of the spinodal decomposition, with the probability
of a general freezing of this process, which can be experimetally observed in
simultaneous IPN formation.Comment: 10 page
On the metal-insulator transition in the two-chain model of correlated fermions
The doping-induced metal-insulator transition in two-chain systems of
correlated fermions is studied using a solvable limit of the t-J model and the
fact that various strong- and weak-coupling limits of the two-chain model are
in the same phase, i.e. have the same low-energy properties. It is shown that
the Luttinger-liquid parameter K_\rho takes the universal value unity as the
insulating state (half-filling) is approached, implying dominant d-type
superconducting fluctuations, independently of the interaction strength. The
crossover to insulating behavior of correlations as the transition is
approached is discussed.Comment: 7 pages, 1 figur
Current reversal and exclusion processes with history-dependent random walks
A class of exclusion processes in which particles perform history-dependent
random walks is introduced, stimulated by dynamic phenomena in some biological
and artificial systems. The particles locally interact with the underlying
substrate by breaking and reforming lattice bonds. We determine the
steady-state current on a ring, and find current-reversal as a function of
particle density. This phenomenon is attributed to the non-local interaction
between the walkers through their trails, which originates from strong
correlations between the dynamics of the particles and the lattice. We
rationalize our findings within an effective description in terms of
quasi-particles which we call front barriers. Our analytical results are
complemented by stochastic simulations.Comment: 5 pages, 6 figure
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