Magnonics is a research field complementary to spintronics, in which quanta of spin waves (magnons) replace electrons as information carriers, promising lower dissipation
. The development of ...ultrafast nanoscale magnonic logic circuits calls for new tools and materials to generate coherent spin waves with frequencies as high, and wavelengths as short, as possible
. Antiferromagnets can host spin waves at terahertz (THz) frequencies and are therefore seen as a future platform for the fastest and the least dissipative transfer of information
. However, the generation of short-wavelength coherent propagating magnons in antiferromagnets has so far remained elusive. Here we report the efficient emission and detection of a nanometer-scale wavepacket of coherent propagating magnons in antiferromagnetic DyFeO
using ultrashort pulses of light. The subwavelength confinement of the laser field due to large absorption creates a strongly non-uniform spin excitation profile, enabling the propagation of a broadband continuum of coherent THz spin waves. The wavepacket contains magnons with a shortest detected wavelength of 125 nm that propagate with supersonic velocities of more than 13 km/s into the material. This source of coherent short-wavelength spin carriers opens up new prospects for THz antiferromagnetic magnonics and coherence-mediated logic devices at THz frequencies.
Resonant ultrafast excitation of infrared-active phonons is a powerful technique with which to control the electronic properties of materials that leads to remarkable phenomena such as the ...light-induced enhancement of superconductivity
, switching of ferroelectric polarization
and ultrafast insulator-to-metal transitions
. Here, we show that light-driven phonons can be utilized to coherently manipulate macroscopic magnetic states. Intense mid-infrared electric field pulses tuned to resonance with a phonon mode of the archetypical antiferromagnet DyFeO
induce ultrafast and long-living changes of the fundamental exchange interaction between rare-earth orbitals and transition metal spins. Non-thermal lattice control of the magnetic exchange, which defines the stability of the macroscopic magnetic state, allows us to perform picosecond coherent switching between competing antiferromagnetic and weakly ferromagnetic spin orders. Our discovery emphasizes the potential of resonant phonon excitation for the manipulation of ferroic order on ultrafast timescales
.
In the paper, we study the two-loop contribution to the effective action of the four-dimensional quantum Yang–Mills theory. We derive a new formula for the contribution in terms of three functions, ...formed from the Green’s function expansion near the diagonal. This result can be applied to different types of regularization. Therefore, we test it by using the dimensional regularization and cutoff ones and show the consistence with the results, obtained in other works.
A
bstract
We study the
η
-invariant of a Dirac operator on a manifold with boundary subject to local boundary conditions with the help of heat kernel methods. In even dimensions, we relate this ...invariant to
η
-invariants of a boundary Dirac operator, while in odd dimension, it is expressed through the index of boundary operators. We stress the necessity of the strong ellipticity condition for the applicability of our methods. We show that the Witten-Yonekura boundary conditions are not strongly elliptic, though they are very close to strongly elliptic ones.
In this paper, we study two-loop contribution to the effective action of a two-dimensional non-linear sigma model. We derive a new formula, which can be applicable to a regularization of general ...type. As examples, we obtain known results for the dimensional regularization and investigate new types of a cutoff one. Also, we discuss non-local contributions and restrictions on the regularization.
We present the results of the prompt, early and afterglow optical observations of five γ-ray bursts (GRBs): GRB 100901A, GRB 100902A, GRB 100905A, GRB 100906A and GRB 101020A. These observations were ...made with the Mobile Astronomical System of TElescope-Robots in Russia (MASTER-II Net), the 1.5-m telescope of the Sierra Nevada Observatory and the 2.56-m Nordic Optical Telescope. For two sources, GRB 100901A and GRB 100906A, we detected optical counterparts and obtained light curves starting before the cessation of γ-ray emission, at 113 and 48 s after the trigger, respectively. Observations of GRB 100906A were conducted in two polarizing filters. Observations of the other three bursts gave the upper limits on the optical flux; their properties are briefly discussed. A more detailed analysis of GRB 100901A and GRB 100906A, supplemented by Swift data, provides the following results and indicates different origins for the prompt optical radiation in the two bursts. The light-curve patterns and spectral distributions suggest that there is a common production site for the prompt optical and high-energy emission in GRB 100901A. The results of the spectral fits for GRB 100901A in the range from optical to X-ray favour power-law energy distributions and a consistent value of the optical extinction in the host galaxy. GRB 100906A produced a smoothly peaking optical light curve, suggesting that the prompt optical radiation in this GRB originated in a front shock. This is supported by a spectral analysis. We have found that the Amati and Ghirlanda relations are satisfied for GRB 100906A. We obtain an upper limit on the value of the optical extinction on the host of GRB 100906A.
Tungsten oxide was electrochemically deposited from a metastable acidic solution of isopolytungstate on glassy carbon electrodes coated by the films of a conducting polymer ...poly-3,4-ethylenedioxythiophene (PEDOT). The formation of PEDOT/WO3 composite films during electrochemical deposition of tungsten oxide into the polymer matrix was gravimetrically monitored by EQCM. The morphology of WO3 deposits was studied using SEM, TEM and EDX analysis, including element mapping and depth concentration profile of main elements. SEM and TEM images of PEDOT/WO3 composites show disperse distribution of WO3 precipitates in the porous matrix of PEDOT, possessing high surface area and pore volume, effective for charge transport. Electrochemical behavior of PEDOT/WO3 was investigated in 0.5 M H2SO4 by cyclic voltammetry, galvanostatic charge-discharge method and electrochemical impedance spectroscopy. The WO3 component in the obtained PEDOT/WO3 composite electrodes exhibited high specific capacitance of 689 F g−1 in the potential range −0.3–0.0 V. The work presents a simple approach for the synthesis of PEDOT/WO3 composites with high values of specific capacitance. The obtained results indicate that PEDOT/WO3 composite could be a promising electrode material for supercapacitor applications.
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•Synthesis of PEDOT/WO3 composites with very fast pseudocapacitive response.•Monitoring of mass change during the synthesis of PEDOT/WO3 composite.•Composite electrodes exhibited high specific capacitance of 689 F g−1•High rate of charge transfer without diffusion limitations up to 0,4 V/s scan rate.
We studied the effect of an indolinone derivative GRS on the development of experimental atherosclerosis in C57BL/6 mice. Atherosclerosis was modeled by intraperitoneal administration of endothelial ...lipoprotein lipase inhibitor Kolliphor P 407 micro Geismar over 5 months. GRS was administered orally in a dose of 10 mg/kg once a day throughout the experiment. In 5 months, the levels of total cholesterol, LDL, and triglycerides in blood serum, as well as histological composition of the ascending aorta were studied. In mice with experimental atherosclerosis, we observed pronounced dyslipidemia with an increase in serum cholesterol, LDL, and triglycerides and accumulation of xanthoma cells in the aorta wall. Repeat administration of GRS did not eliminate dyslipidemia, but prevented an increase in the number of xanthoma cells in the aorta wall (
p
<0.05). The stimulator of soluble guanylate cyclase GRS did not exhibit hypolipidemic activity, but restored impaired endothelial function in the atherosclerosis model and prevented atherosclerotic damage to blood vessels and vascular wall remodeling.
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