Condensed Matter

Ferromagnetism is an exciting phase of matter exhibiting strongly correlated electron behavior and a standard example of spontaneously broken rotational symmetry: below the Curie temperature, atomic magnets in an isotropic single-domain ferromagnetic metal align along a spontaneously chosen direction. The scattering of conduction electrons from thermal perturbations to this spin order, together with electron-electron collisions, mark the material electrical behavior at low temperatures, where the resistivity varies mostly quadratically with the temperature. Around liquid-helium temperatures however, an interesting phenomenon occurs, giving rise to an extra \emph{linear} contribution to the variation of the electrical resistivity with temperature, whose theoretical explanation has encountered problems for a long time. Here I introduce a spin-flip scattering mechanism of conduction electrons in ferromagnetic metals arising from their interaction with the internal magnetic induction and mediated by chiral modes of the crystal lattice vibrations carrying spin 1. This mechanism is able to explain the above anomaly and give a good account of the spin-lattice relaxation times of iron, cobalt and nickel at room temperatures.

Motivated by a recent experimental demonstration of a chiral edge mode in an array of spinning gyroscopes, we theoretically study the coupled gyration modes of topological magnetic solitons, vortices and magnetic bubbles, arranged as a honeycomb lattice. The soliton lattice under suitable conditions is shown to support a chiral edge mode like its mechanical analogue, the existence of which can be understood by mapping the system to the Haldane model for an electronic system. The direction of the chiral edge mode is associated with the topological charge of the constituent solitons, which can be manipulated by an external field or by an electric-current pulse. The direction can also be controlled by distorting the honeycomb lattice. Our results indicate that the lattices of magnetic solitons can serve as reprogrammable topological metamaterials.

We discuss the type of the general macroscopic parity-violating effects, when there is the current along the vortex, which is concentrated in the vortex core. We consider vortices in superfluids, which contain the Weyl points. In the vortex core the positions of the Weyl points form the skyrmion structure. We show that the mass current concentrated in such a core is provided by the spectral flow through the Weyl points according to the Adler-Bell-Jackiw equation for chiral anomaly.

Circulators based on spoof surface plasmon polaritons are designed and analyzed. In the letter, we use blade structure to realize the propagation of SSPPs wave and a matching transition is used to feed energy from coplanar waveguide to the SSPPs. And the circulator shows good nonreciprocal transmission characteristics. The simulation results indicate that in the frequency band from 5 to 6.6 GHz, the isolation degree and return loss basically reaches 15dB and the insertion loss is less than 0.5dB. Moreover, the use of confinement electromagnetic waves can decrease the size of the ferrite and show a broadband characteristic.

Recent discovery of various magnetism in Tsai-type quasicrystalline approximants, in whose alloys rare-earth ions located on icosahedral apices are coupled with each other via the Ruderman--Kittel--Kasuya--Yosida interaction, opens an avenue to find novel magnetism originating from the icosahedral symmetry. Here we investigate classical and quantum magnetic states on an icosahedral cluster within the Heisenberg interactions of all bonds. Simulated annealing and numerical diagonalization are performed to obtain the classical and quantum ground states. We obtain qualitative correspondence of classical and quantum phase diagrams. Our study gives a good starting point to understand the various magnetism in not only quasicrystalline approximants but also quasicrystals.

In the comment I develop a critical analysis of the use of the HVBK method for the study of three-dimensional turbulent flows of superfluids. The conception of the vortex bundles forming the structure of quantum turbulence is controversial and does not justify the use of the HVBK method. In addition, this conception is counterproductive, because it gives incorrect ideas about the structure of the vortex tangle as a set of bundles containing parallel lines. The only type of dynamics of vortex filaments inside these bundles is possible, namely, Kelvin waves running along the filaments. At the same time, as shown in numerous numerical simulations, a vortex tangle consists of a set of entangled vortex loops of different sizes and having a random walk structure. These loops are subject to large deformations (due to highly nonlinear dynamics), they reconnect with each other and with the wall, split and merge, creating a lot of daughter loops. They also bear Kelvin waves on them, but the latter have little impact. I also propose and discuss an alternative variant of study of three-dimensional turbulent flows, in which the vortex line density L(r,t) is not associated with ∇× v s , but it is an independent variable described by a separate equation.

The coherent control of optical phonons has been experimentally demonstrated in various physical systems. While the transient dynamics for optical phonons can be explained by phenomenological models, the coherent control experiment cannot be explained due to the quantum interference. Here, we theoretically propose the generation and detection processes of the optical phonons and experimentally confirm our theoretical model using the diamond optical phonon by the double-pump-probe type experiment.

Two-dimensional superfluidity and quantum turbulence are directly connected to the microscopic dynamics of quantized vortices. However, surface effects have prevented direct observations of coherent vortex dynamics in strongly-interacting two-dimensional systems. Here, we overcome this challenge by confining a two-dimensional droplet of superfluid helium at microscale on the atomically-smooth surface of a silicon chip. An on-chip optical microcavity allows laser-initiation of vortex clusters and nondestructive observation of their decay in a single shot. Coherent dynamics dominate, with thermal vortex diffusion suppressed by six orders-of-magnitude. This establishes a new on-chip platform to study emergent phenomena in strongly-interacting superfluids, test astrophysical dynamics such as those in the superfluid core of neutron stars in the laboratory, and construct quantum technologies such as precision inertial sensors.

We define the time-continuous spin coherent-state path integral in a way that is free from inconsistencies. The proposed definition is used to reproduce known exact results. Such a formalism opens new possibilities for applying approximations with improved accuracy and can be proven useful in a great variety of problems where spin Hamiltonians are used.

In the recently published preprint arXiv:200.02610 Eltsov and L'vov calculated the amplitudes of waves in the Kelvin-wave cascades. This returns us to the rather old, but still unresolved dispute on the role of the tilt symmetry and the locality in the Kelvin-wave cascade. The estimations by Eltsov and L'vov show that the possible nonlocality of the energy flux in the Kelvin-wave cascade has no essential effect on the Kelvin-wave cascade in the 3D vortex tangle.