Theoretical prediction of rotating magnon wavepacket in ferromagnets

We theoretically show that the magnon wavepacket has a rotational motion in two ways; a self-rotation and a motion along the boundary of the sample (edge current). They are similar to cyclotron motion of electrons, but unlike electrons the magnons have no charge and the rotation is not due to Lorenz force. These rotational motions are caused by the Berry phase in momentum space from magnon band structure. Furthermore, these rotational motions of the magnon give an additional correction term to the magnon Hall effect. We also discuss the Berry curvature effect in the classical limit of long-wavelength magnetostatic spin waves having macroscopic coherence length.Comment: 4pages, 2figures, accepted for publication in Phys. Rev. Let

Uncertainty principle for proper time and mass

We review Bohr's reasoning in the Bohr-Einstein debate on the photon box experiment. The essential point of his reasoning leads us to an uncertainty relation between the proper time and the rest mass of the clock. It is shown that this uncertainty relation can be derived if only we take the fundamental point of view that the proper time should be included as a dynamic variable in the Lagrangian describing the system of the clock. Some problems and some positive aspects of our approach are then discussed.Comment: 15 pages, accepted for publication in J. Math. Phy

Chiral spin-wave edge modes in dipolar magnetic thin films

Based on a linearized Landau-Lifshitz equation, we show that two-dimensional periodic allay of ferromagnetic particles coupled with magnetic dipole-dipole interactions supports chiral spin-wave edge modes, when subjected under the magnetic field applied perpendicular to the plane. The mode propagates along a one-dimensional boundary of the system in a unidirectional way and it always has a chiral dispersion within a band gap for spin-wave volume modes. Contrary to the well-known Damon-Eshbach surface mode, the sense of the rotation depends not only on the direction of the field but also on the strength of the field; its chiral direction is generally determined by the sum of the so-called Chern integers defined for spin-wave volume modes below the band gap. Using simple tight-binding descriptions, we explain how the magnetic dipolar interaction endows spin-wave volume modes with non-zero Chern integers and how their values will be changed by the field.Comment: 18 pages, 16 figures, some trivial typo in equations are fixe

Topological chiral magnonic edge mode in a magnonic crystal

Topological phases have been explored in various fields in physics such as spintronics, photonics, liquid helium, correlated electron system and cold-atomic system. This leads to the recent foundation of emerging materials such as topological band insulators, topological photonic crystals and topological superconductors/superfluid. In this paper, we propose a topological magnonic crystal which provides protected chiral edge modes for magnetostatic spin waves. Based on a linearized Landau-Lifshitz equation, we show that a magnonic crystal with the dipolar interaction acquires spin-wave volume-mode band with non-zero Chern integer. We argue that such magnonic systems are accompanied by the same integer numbers of chiral spin-wave edge modes within a band gap for the volume-mode bands. In these edge modes, the spin wave propagates in a unidirectional manner without being scattered backward, which implements novel fault-tolerant spintronic devices.Comment: 12 pages, 7 figure

Safety of smoke generated by Japanese moxa upon combustion

AbstractIntroductionMoxibustion is an ancient method of traditional medicine (along with acupuncture) using moxa, or processed mugwort leaves. Both the smoke and heat generated by burning moxa are considered to have therapeutic effects. However, recently there have been reports of harmful substances released in smoke from everyday objects such as scented candles or incense. Therefore it appeared to be important to evaluate the safety of products resulting from the combustion of moxa.MethodsWe used three types of commonly used moxa. Experiments were conducted by lighting moxa which had been classified according to their level of refinement. Gases released were collected after igniting moxa. A gas chromatograph mass spectrometer (GC/MS) was used for both qualitative and quantitative analysis. Standard conditions for Japanese therapeutic environments were employed.Results1,3-butadiene was present from the smoke at the highest level of concentrations of substances governed by assorted indoor air quality and environmental standards (1,3-butadiene, benzene, toluene, ethylbenzene, and xylene) and fell below maximum values. Also, simulation in an indoor environment with 1,3-butadiene was safely within indoor environmental standards.ConclusionOur simulation results have shown that quantities of harmful substances released upon combustion of moxa during normal clinical therapy of Japan are below maximum levels. Hence are safe for both patient and practitioner. However we detected few amounts of harmful substances released from moxa. These harmful substances are invariably generated upon combustion, although varieties and quantities vary according to substance. So measures to maintain an appropriately safe work environment must be practiced, even though safety was confirmed

Linearly Polarized Coherent Emission from Relativistic Magnetized Ion-Electron Shocks

「富岳」で高速電波バーストの再現に成功 --宇宙最大の電波爆発の起源に迫る--. 京都大学プレスリリース. 2024-02-05.Fast radio bursts (FRBs) are millisecond transient astrophysical phenomena and bright at radio frequencies. The emission mechanism, however, remains unsolved yet. One scenario is a coherent emission associated with the magnetar flares and resulting relativistic shock waves. Here, we report unprecedentedly large-scale simulations of relativistic magnetized ion-electron shocks, showing that strongly linear-polarized electromagnetic waves are excited. The kinetic energy conversion to the emission is so efficient that the wave amplitude is responsible for the brightness. We also find a polarization angle swing reflecting shock front modulation, implicating the polarization property of some repeating FRBs. The results support the shock scenario as an origin of the FRBs