23,257 research outputs found
Pairs of orthogonal countable ordinals
We characterize pairs of orthogonal countable ordinals. Two ordinals
and are orthogonal if there are two linear orders and on the
same set with order types and respectively such that the
only maps preserving both orders are the constant maps and the identity map. We
prove that if and are two countable ordinals, with , then and are orthogonal if and only if either
or and
Atomic diffraction from nanostructured optical potentials
We develop a versatile theoretical approach to the study of cold-atom
diffractive scattering from light-field gratings by combining calculations of
the optical near-field, generated by evanescent waves close to the surface of
periodic nanostructured arrays, together with advanced atom wavepacket
propagation on this optical potential.Comment: 8 figures, 10 pages, submitted to Phys. Rev.
Stripe, checkerboard, and liquid-crystal ordering from anisotropic p-orbital Fermi surfaces in optical lattices
We study instabilities of single-species fermionic atoms in the p-orbital
bands in two-dimensional optical lattices at noninteger filling against
interactions. Charge density wave and orbital density wave orders with stripe
or checkerboard patterns are found for attractive and repulsive interactions,
respectively. The superfluid phase, usually expected of attractively
interacting fermions, is strongly suppressed. We also use field theory to
analyze the possible phase-transitions from orbital stripe order to
liquid-crystal phases and obtain the phase diagram. The condition of
nearly-perfect Fermisurface nesting, which is key to the above results, is
shown robustly independent of fermion fillings in such p-orbital systems, and
the momentum of density wave oscillation is highly tunable.
Such remarkable features show the promise of making those exotic orbital
phases, which are of broad interest in condensed-matter physics, experimentally
realizable with optical lattice gases.Comment: final version, 8 pages, 5 figure
Atomically thin dilute magnetism in Co-doped phosphorene
Two-dimensional dilute magnetic semiconductors can provide fundamental
insights in the very nature of magnetic orders and their manipulation through
electron and hole doping. Despite the fundamental physics, due to the large
charge density control capability in these materials, they can be extremely
important in spintronics applications such as spin valve and spin-based
transistors. In this article, we studied a two-dimensional dilute magnetic
semiconductors consisting of phosphorene monolayer doped with cobalt atoms in
substitutional and interstitial defects. We show that these defects can be
stabilized and are electrically active. Furthermore, by including holes or
electrons by a potential gate, the exchange interaction and magnetic order can
be engineered, and may even induce a ferromagnetic-to-antiferromagnetic phase
transition in p-doped phosphorene.Comment: 7 pages, 4 colorful figure
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