Search

Magnetic skyrmion bags are composite topological spin textures with arbitrary topological charges. Here, we computationally study the transient rotational motion of skyrmion bags, which is characterized by a global rotation of inner skyrmions around the central point. Distinct from conventional rotational modes found in skyrmions, the observed rotation is a forced motion associated with the breathing mode induced solely by vertical microwave fields. The driving force behind this rotation originates from the interactions between outer and inner skyrmions, with the angular velocity determined by the phase difference resulting from their asynchronous breathing behaviors. It is also found that skyrmion bags with larger skyrmion numbers are more conducive to the occurrence of the rotation. Our results are useful for understanding the cluster dynamics of complex topological spin textures driven by dynamic fields. [ABSTRACT FROM AUTHOR]

Given a partial action α of a groupoid G on a ring R, we study the associated partial skew groupoid ring R ⋊ α G , which carries a natural G-grading. We show that there is a one-to-one correspondence between the G-invariant ideals of R and the graded ideals of the G-graded ring R ⋊ α G . We provide sufficient conditions for primeness, and necessary and sufficient conditions for simplicity of R ⋊ α G . We show that every ideal of R ⋊ α G is graded if and only if α has the residual intersection property. Furthermore, if α is induced by a topological partial action θ, then we prove that minimality of θ is equivalent to G-simplicity of R, topological transitivity of θ is equivalent to G-primeness of R, and topological freeness of θ on every closed invariant subset of the underlying topological space is equivalent to α having the residual intersection property. As an application, we characterize condition (K) for an ultragraph in terms of topological properties of the associated partial action and in terms of algebraic properties of the associated ultragraph algebra. [ABSTRACT FROM AUTHOR]

We investigate the ultrafast spin dynamics of the prototypical topological insulator Bi2Se3 using time-resolved Kerr rotation (polarization-change) measurements across near-infrared wavelengths. The Kerr rotation angle Δ θ K of Bi2Se3 was found to significantly depend on the photon energy around a resonance transition (∼ 1.0 eV) of bulk states, as well as the ellipticity of the pump light, in the presence of spin excitation. The observed photon-energy dependence of Δ θ K can be well simulated by assuming spin-dependent refractive-index changes in the presence of bandgap renormalization and state-filling effect upon photoexcitation. Our study delivers comprehensive insights into the opto-spintronic properties of bulk Bi2Se3 and the fundamental physical processes underlying polarization changes. These findings are expected to be crucial in developing ultrafast magneto-optical memory devices, which can perform read-and-write operations in the terahertz regime. [ABSTRACT FROM AUTHOR]

Advancements in photonics technologies have significantly enhanced their capability to facilitate experiments involving quantum light, even at room temperature. Nevertheless, fully integrating photonic chips that include quantum light sources, effective manipulation and transport of light minimizing losses, and appropriate detection systems remains an ongoing challenge. Topological photonic systems have emerged as promising platforms to protect quantum light properties during propagation, beyond merely preserving light intensity. In this work, we delve into the dynamics of non-classical light traversing a Su-Schrieffer-Heeger photonic lattice with topological domain walls. Our focus centers on how topology influences the quantum properties of light as it moves across the array. By precisely adjusting the spacing between waveguides, we achieve dynamic repositioning and interaction of domain walls, facilitating effective beam-splitting operations. Our findings demonstrate high-fidelity transport of non-classical light across the lattice, replicating known results that are now safeguarded by the topology of the system. This protection is especially beneficial for quantum communication protocols with continuous variable states. Our study enhances the understanding of light dynamics in topological photonic systems and paves the way for high-fidelity, topology-protected quantum communication. [ABSTRACT FROM AUTHOR]

The abundant topological magnetic textures in three-dimensional systems provide opportunities to investigate the fundamental spin dynamics and realize spintronic applications. The dynamics of such magnetic textures have however rarely been studied, especially for those driven by spin waves, which allow applications with ultralow energy consumption and ease of implementation even in insulating systems. Here, we report our micromagnetic simulations on the spin-wave-driven dynamics of a skyrmion tube (SkT) and chiral bobber (ChB) in a thick magnetic film. We predict tornado-like dynamics in both SkT and ChB, where the topological centers present a lateral rotation with the rotation centers forming a distorted profile in the thickness direction. While the velocity of SkT scales with the driving power, the ChB motion presents a threshold in the driving field, which is found to depend linearly on its penetration length. This distinct behavior could be useful to differentiate ChB from SkT and estimate its penetration length experimentally. The magnetic dynamics driven by spin waves can be useful for low-consumption devices, which is however still largely unexplored in three-dimensional system. Here, the authors find, using micromagnetic simulations, spin-wave-driven tornado-like dynamics of skyrmion tube and chiral bobber in thick magnetic films. [ABSTRACT FROM AUTHOR]

Any affine map on the (n + 1)-dimensional Euclidean space gives rise to a natural map on the n-dimensional sphere whose dynamical aspects are not so well-studied in the literature. We explore the dynamical aspects of these maps by investigating about their distality and expansivity. [ABSTRACT FROM AUTHOR]

We experimentally and theoretically study the dynamics of a one-dimensional array of pendula with a mild spatial gradient in their self-frequency and where neighboring pendula are connected with weak and alternating coupling. We map their dynamics to the topological Su-Schrieffer-Heeger model of charged quantum particles on a lattice with alternating hopping rates in an external electric field. By directly tracking the dynamics of a wave-packet in the bulk of the lattice, we observe Bloch oscillations, Landau-Zener transitions, and coupling between the isospin (i.e., the inner wave function distribution within the unit cell) and the spatial degrees of freedom (the distribution between unit cells). We then use Bloch oscillations in the bulk to directly measure the nontrivial global topological phase winding and local geometric phase of the band. We measure an overall evolution of 3.1 ± 0.2 radians for the geometrical phase during the Bloch period, consistent with the expected Zak phase of π. Our results demonstrate the power of classical analogs of quantum models to directly observe the topological properties of the band structure and shed light on the similarities and the differences between quantum and classical topological effects. [ABSTRACT FROM AUTHOR]

Features of the dynamics of topological defects in an electroconvective structure formed in a π/2-twisted nematic liquid crystal have been studied. The electroconvective structure (Williams domains) is a system of rolls similar to the system of convective cells in thermal convection. Hydrodynamic flows in rolls of the twisted nematic liquid crystal are helicoidal because the axial velocity component existing in addition to the tangential component has opposite directions in the neighboring rolls. This feature is responsible for the formation of stable localized extended objects—linear defects—oriented normally to Williams domains. The continuity condition for a helicoidal flow of an anisotropic liquid in twisted nematic liquid crystals prevents the decay of a linear defect into single dislocations. The length of the linear defect and the number of dislocations in it are controlled by an ac voltage applied to a liquid crystal cell. In contrast to the case of planar orientation, where linear defects decay into single dislocations with increasing applied voltage, zigzag oscillations appear in this case, but the structure of domains remains stationary. The boundaries between zig and zag regions in the core of the linear defect are dislocations with the topological charges S = +1 and –1. An "elementary" decay of a dislocation with the topological charge S = +1 (kink) into the dislocation with S = –1 (antikink) and two dislocations the topological charges S = +1 has been found for the first time in the linear defect of a certain length. The decay of the topological defect is possibly due to the appearance of the local instability of the orientational twist mode of the director n in the defect core caused by the critical growth of hydrodynamic fluctuations with increasing applied voltage. It has been shown that the detected decay of the topological soliton is qualitatively well described by the perturbed sine-Gordon eq-uation. [ABSTRACT FROM AUTHOR]

The consideration of homomorphisms ("extensions") of minimal flows is central to topological dynamics. Building upon two earlier papers of the first author, with two different collaborators, we study open extensions of minimal flows. These are classified using maximally highly proximal generators, certain closed subsets of the universal minimal flow. The orbit closures of such in the space of closed subsets are the maximally highly proximal minimal flows. Given a maximally highly proximal generator C , the action of the universal minimal flow on a space gives rise to a " C extension" (the inverse images are determined by C). These are open and every open homomorphism is in fact a C extension for some MHP generator C. This generalizes the classical special case of RIC extensions. Moreover, the open extensions can be represented as quasi-factors (minimal sets in the space of closed subsets). We also consider a category whose objects are extensions of minimal flows and define the morphisms of these. [ABSTRACT FROM AUTHOR]