141 research outputs found
Cavity Optomechanics of Topological Spin Textures in Magnetic Insulators
Collective dynamics of topological magnetic textures can be thought of as a
massive particle moving in a magnetic pinning potential. We demonstrate that
inside a cavity resonator this effective mechanical system can feel the
electromagnetic radiation pressure from cavity photons through the
magneto-optical inverse Faraday and Cotton-Mouton effects. We estimate values
for the effective parameters of the optomechanical coupling for two spin
textures -- a Bloch domain wall and a chiral magnetic soliton lattice. The
soliton lattice has magnetic chirality, so that in circularly polarized light
it behaves like a chiral particle with the sign of the optomechanical coupling
determined by the helicity of the light and chirality of the lattice. Most
interestingly, we find a level attraction regime for the soliton lattice, which
is tunable through an applied magnetic field.Comment: 7 pages, 3 figures, published versio
Excitation of magnon spin photocurrents in antiferromagnetic insulators
In the circular photogalvanic effect, circularly polarized light can produce
a direct electron photocurrent in metals and the direction of the current
depends on the polarization. We suggest that an analogous nonlinear effect
exists for antiferromagnetic insulators wherein the total spin of light and
spin waves is conserved. In consequence, a spin angular momentum is expected to
be transfered from photons to magnons so that a circularly polarized
electromagnetic field will generate a direct magnon spin current. The direction
of the current is determined by the helicity of the light. We show that this
resonant effect appears as a second order light-matter interaction. We find
also a geometric contribution to the spin photocurrent, which appears for
materials with complex lattice structures and Dzyaloshinskii-Moriya
interactions.Comment: 10 pages, 2 figures, published versio
Functional renormalization-group approach to the Pokrovsky-Talapov model via modified massive Thirring fermion model
A possibility of the topological Kosterlitz-Thouless~(KT) transition in the
Pokrovsky-Talapov~(PT) model is investigated by using the functional
renormalization-group (RG) approach by Wetterich. Our main finding is that the
nonzero misfit parameter of the model, which can be related with the linear
gradient term (Dzyaloshinsky-Moriya interaction), makes such a transition
impossible, what contradicts the previous consideration of this problem by
non-perturbative RG methods. To support the conclusion the initial PT model is
reformulated in terms of the 2D theory of relativistic fermions using an
analogy between the 2D sine-Gordon and the massive Thirring models. In the new
formalism the misfit parameter corresponds to an effective gauge field that
enables to include it in the RG procedure on an equal footing with the other
parameters of the theory. The Wetterich equation is applied to obtain flow
equations for the parameters of the new fermionic action. We demonstrate that
these equations reproduce the KT type of behavior if the misfit parameter is
zero. However, any small nonzero value of the quantity rules out a possibility
of the KT transition. To confirm the finding we develop a description of the
problem in terms of the 2D Coulomb gas model. Within the approach the breakdown
of the KT scenario gains a transparent meaning, the misfit gives rise to an
effective in-plane electric field that prevents a formation of bound
vortex-antivortex pairs.Comment: 12 pages, 3 figure
Spin-wave chirality and its manifestations in antiferromagnets
As first demonstrated by Tang and Cohen in chiral optics, the asymmetry in
the rate of electromagnetic energy absorption between left and right
enantiomers is determined by an optical chirality density [1]. Here, we
demonstrate that this effect can exist in magnetic spin systems. By
constructing a formal analogy with electrodynamics, we show that in
antiferromagnets with broken chiral symmetry the asymmetry in local spin-wave
energy absorption is proportional to a spin-wave chirality density, which is a
direct counterpart of optical zilch. We propose that injection of a pure spin
current into an antiferromagnet may serve as a chiral symmetry breaking
mechanism, since its effect in the spin-wave approximation can be expressed in
terms of additional Lifshitz invariants. We use linear response theory to show
that the spin current induces a nonequilibrium spin-wave chirality density.Comment: 6 pages (plus Supplemental Material, 6 pages), 1 figure, published
versio
Theory of magnetoelastic resonance in a mono-axial chiral helimagnet
We study magnetoelastic resonance phenomena in a mono-axial chiral helimagnet
belonging to hexagonal crystal class. By computing the spectrum of coupled
elastic wave and spin wave, it is demonstrated how hybridization occurs
depending on their chirality. Specific features of the magnetoelastic resonance
are discussed for the conical phase and the soliton lattice phase stabilized in
the mono-axial chiral helimagnet. The former phase exhibits appreciable
non-reciprocity of the spectrum, the latter is characterized by a
multi-resonance behavior. We propose that the non-reciprocal spin wave around
the forced-ferromagnetic state has potential capability to convert the linearly
polarized elastic wave to circularly polarized one with the chirality opposite
to the spin wave chirality.Comment: 12 pages, 5 figures, Accepted in Phys. Rev.
Smart Camp: Building Scalable and Highly Available IT-Infrastructures
The Western Australian resources boom has created a demand for a large amount of domestic accommodations, known as mining camps. However, due to the absent infrastructure within the remote regions of Australia, the energy supply of these mining camps is expensive. In order to reduce the electricity consumption of the mining camps, the Smart Camp project was initiated. The system infrastructure consists of a home automation based controller, placed in each mining accommodation unit to reduce energy consumption, and a centralized management unit, coordinating the controllers. Due to the fact that the size and complexity of mining camps may grow over time, the provided infrastructure of the management unit has to be able to evolve. One possible solution is to design a system in the context of high availability and horizontal scalability. This paper proposes a horizontally scalable and high availability infrastructural concept, in the context of the Smart Camp project. This concept also utilizes cost effective open source solutions running on commodity hardware. Within the context of horizontal scalability and reliability, this paper provides an applied research outline of some of the real world considerations, such as open source based high availability, load balancing, and distributed database solutions
On C*-algebras generated by pairs of q-commuting isometries
We consider the C*-algebras O_2^q and A_2^q generated, respectively, by
isometries s_1, s_2 satisfying the relation s_1^* s_2 = q s_2 s_1^* with |q| <
1 (the deformed Cuntz relation), and by isometries s_1, s_2 satisfying the
relation s_2 s_1 = q s_1 s_2 with |q| = 1. We show that O_2^q is isomorphic to
the Cuntz-Toeplitz C*-algebra O_2^0 for any |q| < 1. We further prove that
A_2^{q_1} is isomorphic to A_2^{q_2} if and only if either q_1 = q_2 or q_1 =
complex conjugate of q_2. In the second part of our paper, we discuss the
complexity of the representation theory of A_2^q. We show that A_2^q is *-wild
for any q in the circle |q| = 1, and hence that A_2^q is not nuclear for any q
in the circle.Comment: 18 pages, LaTeX2e "article" document class; submitted. V2 clarifies
the relationships between the various deformation systems treate
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