243,880 research outputs found
Modelling spin waves in noncollinear antiferromagnets: spin-flop states, spin spirals, skyrmions and antiskyrmions
Spin waves in antiferromagnetic materials have great potential for
next-generation magnonic technologies. However, their properties and their
dependence on the type of ground-state antiferromagnetic structure are still
open questions. Here, we investigate theoretically spin waves in one- and
two-dimensional model systems with a focus on noncollinear antiferromagnetic
textures such as spin spirals and skyrmions of opposite topological charges. We
address in particular the nonreciprocal spin excitations recently measured in
bulk antiferromagnet -- utilizing
inelastic neutron scattering experiments [Phys.\ Rev.\ Lett.\ \textbf{119},
047201 (2017)], where we help to characterize the nature of the detected
spin-wave modes. Furthermore, we discuss how the Dzyaloshinskii-Moriya
interaction can lift the degeneracy of the spin-wave modes in antiferromagnets,
resembling the electronic Rashba splitting. We consider the spin-wave
excitations in antiferromagnetic spin-spiral and skyrmion systems and discuss
the features of their inelastic scattering spectra. We demonstrate that
antiskyrmions can be obtained with an isotropic Dzyaloshinskii-Moriya
interaction in certain antiferromagnets.Comment: 26 pages, 9 figure
First-principles investigation of spin wave dispersions in surface-reconstructed Co thin films on W(110)
We computed spin wave dispersions of surface-reconstructed Co films on the
W(110) surface in the adiabatic approximation. The magnetic exchange
interactions are obtained via first-principles electronic structure
calculations using the Korringa-Kohn-Rostoker Green function method. We analyze
the strength and oscillatory behavior of the intralayer and interlayer magnetic
interactions and investigate the resulting spin wave dispersions as a function
of the thickness of Co films. In particular, we highlight and explain the
strong impact of hybridization of the electronic states at the Co-W interface
on the magnetic exchange interactions and on the spin wave dispersions. We
compare our results to recent measurements based on electron energy loss
spectroscopy [E. Michel, H. Ibach, and C.M. Schneider, Phys. Rev. B 92, 024407
(2015)]. Good overall agreement with experimental findings can be obtained by
considering the possible overestimation of the spin splitting, stemming from
the local spin density approximation, and adopting an appropriate correction.Comment: 14 pages, 14 figure
Characteristic functions on the boundary of a planar domain need not be traces of least gradient functions
Given a smooth bounded planar domain, we construct a compact set on the
boundary s.t. its characteristic function is not the trace of a least gradient
function. This generalize the construction of Spradlin and Tamasan [ST14] on
the disc
Introduction to Gauge Theory of Gravitation
The fundamental interactions of nature, the electroweak and the quantum
chromodynamics, are described in the Standard Model by the Gauge Theory under
internal symmetries that maintain the invariance of the functional action. The
fundamental interaction of gravitation is very well described by Einstein's
General Relativity in a Riemannian spacetime metric, but General Relativity has
been over time a gravitational field theory apart from the Standard Model. The
theory of Gauge allows under symmetries of the group of Poincar\'e to impose
invariances in the functional of the action of the spinor field that result in
the gravitational interaction with the fermions. In this approach the
gravitational field, besides being described by the equation similar to General
Relativity, also brings a spin-gravitational interaction in a Riemann-Cartan
spacetime.Comment: 23 page
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