17 research outputs found
Generic ordering of structural transitions in quasi-one-dimensional Wigner crystals
We investigate the dependence of the structural phase transitions in an
infinite quasi-one-dimensional system of repulsively interacting particles on
the profile of the confining channel. Three different functional expressions
for the confinement potential related to real experimental systems are used
that can be tuned continuously from a parabolic to a hard-wall potential in
order to find a thorough understanding of the ordering of the chain-like
structure transitions. We resolve the longstanding issue why the most theories
predicted a 1-2-4-3-4 sequence of chain configurations with increasing density,
while some experiments found the 1-2-3-4 sequence.Comment: 7 pages, 5 figure
Structural transitions in vertically and horizontally coupled parabolic channels of Wigner crystals
Structural phase transitions in two vertically or horizontally coupled
channels of strongly interacting particles are investigated. The particles are
free to move in the -direction but are confined by a parabolic potential in
the -direction. They interact with each other through a screened power-law
potential (). In vertically coupled systems the channels
are stacked above each other in the direction perpendicular to the
-plane, while in horizontally coupled systems both channels are aligned
in the confinement direction. Using Monte Carlo (MC) simulations we obtain the
ground state configurations and the structural transitions as a function of the
linear particle density and the separation between the channels. At zero
temperature the vertically coupled system exhibits a rich phase diagram with
continuous and discontinuous transitions. On the other hand the vertically
coupled system exhibits only a very limited number of phase transitions due to
its symmetry. Further we calculated the normal modes for the Wigner crystals in
both cases. From MC simulations we found that in the case of vertically coupled
systems the zigzag transition is only possible for low densities. A
Ginzburg-Landau theory for the zigzag transition is presented, which predicts
correctly the behavior of this transition from which we interpret the
structural phase transition of the Wigner crystal through the reduction of the
Brillouin zone.Comment: 9 pages, 13 figure
Magnetic particles confined in a modulated channel: structural transitions tunable by tilting a magnetic field
The ground state of colloidal magnetic particles in a modulated channel are
investigated as function of the tilt angle of an applied magnetic field. The
particles are confined by a parabolic potential in the transversal direction
while in the axial direction a periodic substrate potential is present. By
using Monte Carlo (MC) simulations, we construct a phase diagram for the
different crystal structures as a function of the magnetic field orientation,
strength of the modulated potential and the commensurability factor of the
system. Interestingly, we found first and second order phase transitions
between different crystal structures, which can be manipulated by the
orientation of the external magnetic field. A re-entrant behavior is found
between two- and four-chain configurations, with continuous second order
transitions. Novel configurations are found consisting of frozen in solitons.
By changing the orientation and/or strength of the magnetic field and/or the
strength and the spatial frequency of the periodic substrate potential, the
system transits through different phases.Comment: Submitted to Phys. Rev. E (10 pages, 12 figures
Ginzburg-Landau theory of the zig-zag transition in quasi-one-dimensional classical Wigner crystals
We present a mean-field description of the zig-zag phase transition of a
quasi-one-dimensional system of strongly interacting particles, with
interaction potential , that are confined by a power-law
potential (). The parameters of the resulting one-dimensional
Ginzburg-Landau theory are determined analytically for different values of
and . Close to the transition point for the zig-zag phase
transition, the scaling behavior of the order parameter is determined. For
the zig-zag transition from a single to a double chain is of second
order, while for the one chain configuration is always unstable and
for the one chain ordered state becomes unstable at a certain
critical density resulting in jumps of single particles out of the chain.Comment: 12 pages, 11 figure