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

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

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

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