3,454 research outputs found
Graphene under the influence of Aharonov-Bohm flux and constant magnetic field
Investigation of real two-dimensional systems with Dirac-like electronic
behavior under the influence of magnetic field is challenging and leads to many
interesting physical results. In this paper we study 2D graphene model with a
particular form of magnetic field as a superposition of a homogeneous field and
an Aharonov-Bohm vortex. For this configuration, electronic wave functions and
energy spectrum were obtained and it was shown that the magnetic Aharonov-Bohm
vortex plays the role of a charge impurity. As a demonstration of vacuum
properties of the system, vacuum current, as well as an electric current, is
calculated and their representation for particular limiting cases of magnetic
field is obtained
Laser-induced topological transitions in phosphorene with inversion symmetry
Recent ab initio calculations and experiments reported
insulating-semimetallic phase transitions in multilayer phosphorene under a
perpendicular dc field, pressure or doping, as a possible route to realize
topological phases. In this work, we show that even a monolayer phosphorene may
undergo Lifshitz transitions toward semimetallic and topological insulating
phases, provided it is rapidly driven by in-plane time-periodic laser fields.
Based on a four-orbital tight-binding description, we give an
inversion-symmetry-based prescription in order to apprehend the topology of the
photon-renormalized band structure, up to the second order in the
high-frequency limit. Apart from the initial band insulating behavior, two
additional phases are thus identified. A semimetallic phase with massless Dirac
electrons may be induced by linear polarized fields, whereas elliptic polarized
fields are likely to drive the material into an anomalous quantum Hall phase.Comment: Includes Supplemental Materia
Dynamical and Reversible Control of Topological Spin Textures
Recent observations of topological spin textures brought spintronics one step
closer to new magnetic memories. Nevertheless, the existence of Skyrmions, as
well as their stabilization, require very specific intrinsic magnetic
properties which are usually fixed in magnets. Here we address the possibility
to dynamically control their intrinsic magnetic interactions by varying the
strength of a high-frequency laser field. It is shown that drastic changes can
be induced in the antiferromagnetic exchange interactions and the latter can
even be reversed to become ferromagnetic, provided the direct exchange is
already non-negligible in equilibrium as predicted, for example, in Si doped
with C, Sn, or Pb adatoms. In the presence of Dzyaloshinskii-Moriya
interactions, this enables us to tune features of ferromagnetic Skyrmions such
as their radius, making them easier to stabilize. Alternatively, such
topological spin textures can occur in frustrated triangular lattices. Then, we
demonstrate that a high-frequency laser field can induce dynamical frustration
in antiferromagnets, where the degree of frustration can subsequently be tuned
suitably to drive the material toward a Skyrmionic phase
Long-term planning versus short-term planning in the asymptotical location problem
Given the probability measure over the given region , we consider the optimal location of a set composed by
points \Om in order to minimize the average distance \Sigma\mapsto \int_\Om
\dist(x,\Sigma) d\nu (the classical optimal facility location problem). The
paper compares two strategies to find optimal configurations: the long-term one
which consists in placing all points at once in an optimal position, and
the short-term one which consists in placing the points one by one adding at
each step at most one point and preserving the configuration built at previous
steps. We show that the respective optimization problems exhibit qualitatively
different asymptotic behavior as , although the optimization costs
in both cases have the same asymptotic orders of vanishing.Comment: for more pictures and some movies as well, see
http://www.sissa.it/~brancoli
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