Terahertz light-driven coupling of antiferromagnetic spins to lattice Mashkovich, Evgeny A; Grishunin, Kirill A; Dubrovin, Roman M ...
Science (American Association for the Advancement of Science),
2021-Dec-24, 2021-12-24, 20211224, Letnik:
374, Številka:
6575
Journal Article
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Understanding spin-lattice coupling represents a key challenge in modern condensed matter physics, with crucial importance and implications for ultrafast and two-dimensional magnetism. The efficiency ...of angular momentum and energy transfer between spins and the lattice imposes fundamental speed limits on the ability to control spins in spintronics, magnonics, and magnetic data storage. We report on an efficient nonlinear mechanism of spin-lattice coupling driven by terahertz light pulses. A nearly single-cycle terahertz pulse resonantly interacts with a coherent magnonic state in the antiferromagnet cobalt difluoride (CoF
) and excites the Raman-active terahertz phonon. The results reveal the distinctive functionality of antiferromagnets that allows ultrafast spin-lattice coupling using light.
Abstract Understanding spin-lattice interactions in antiferromagnets is a critical element of the fields of antiferromagnetic spintronics and magnonics. Recently, coherent nonlinear phonon dynamics ...mediated by a magnon state were discovered in an antiferromagnet. Here, we suggest that a strongly coupled two-magnon-one phonon state in this prototypical system opens a novel pathway to coherently control magnon-phonon dynamics. Utilizing intense narrow-band terahertz (THz) pulses and tunable magnetic fields up to μ 0 H ext = 7 T, we experimentally realize the conditions of magnon-phonon Fermi resonance in antiferromagnetic CoF 2 . These conditions imply that both the spin and the lattice anharmonicities harvest energy from the transfer between the subsystems if the magnon eigenfrequency f m is half the frequency of the phonon 2 f m = f ph . Performing THz pump-infrared probe spectroscopy in conjunction with simulations, we explore the coupled magnon-phonon dynamics in the vicinity of the Fermi-resonance and reveal the corresponding fingerprints of nonlinear interaction facilitating energy exchange between these subsystems.
Experimental results on temperature dependences of the low-frequency dielectric permittivity of the group of magnetic fluoroperovskites with different crystal and magnetic structures are presented. ...Orthorhombic NaCoF
3
and NaNiF
3
, cubic RbFeF
3
, hexagonal RbNiF
3
and tetragonal K
2
CoF
4
and K
2
NiF
4
were investigated. The analysis of experimental results in combination with those of our previous studies of other fluoroperovskites was carried out taking into account the influence of the spontaneous magnetodielectric effect on lattice dynamics. It revealed the role of the spin-phonon coupling and the anharmonic contribution, which leads an increase of dielectric permittivity at heating, and contribution of the hidden structural instability manifested as an increase of the dielectric permittivity at cooling. It was established that the relative contributions of these three main mechanisms to the temperature dependence of dielectric permittivity are significantly different in all fluoroperovskites under study but they are well correlated with the tolerance factor
t
, which characterizes a relation between ionic radii and is a measure of stability of AMF
3
perovskite crystal structure. The obtained results and their analysis reliably demonstrate that the low-frequency dielectric spectroscopy is a highly sensitive method to study particular features of the lattice dynamics of fluoroperovskites at magnetic and structural phase transitions.
Psana (Photon Science Analysis) is a software package that is used to analyze data produced by the Linac Coherent Light Source X‐ray free‐electron laser at the SLAC National Accelerator Laboratory. ...The project began in 2011, is written primarily in C++ with some Python, and provides user interfaces in both C++ and Python. Most users use the Python interface. The same code can be run in real time while data are being taken as well as offline, executing on many nodes/cores using MPI for parallelization. It is publicly available and installable on the RHEL5/6/7 operating systems.
The software used to analyze data produced at the Linac Coherent Light Source X‐ray free‐electron laser is described.
This article examines the issue of forecasting the time series of server systems and suggests applying the triple exponential smoothing model to solve this problem. It presents a mathematical ...formulation of the problem and describes the specifics of forecasting the time series of server systems. After this the article gives a comparative analysis of the autoregressive, neural network and exponential smoothing models in terms of their application to this problem. It argues that the triple exponential smoothing model (Holt-Winters method) offers a number of advantages when modelling the time series of server systems. It then provides experimental research to evaluate the accuracy of the Holt-Winters method with respect to the indicated time series. The research shows that the triple exponential smoothing model exhibits high results and can be applied to the solution of practical problems.
In the last two decades copper metaborate CuB
2
O
4
with a unique noncentrosymmetric crystal structure has become the subject of active research due to its unusual magnetic and optical properties. ...We consider the propagation and absorption of light in CuB
2
O
4
based on the solution of Maxwell’s equations. We present an overview of the main results on the investigation of the phonon spectrum using infrared and Raman spectroscopy. Studies in the region of electronic transitions in Cu
2+
ions in the crystal field have allowed the separation of contributions to the optical absorption from copper ions in inequivalent positions. A splitting of zero-phonon absorption lines in a magnetic field has been detected, and these results have received a theoretical explanation in terms of the exciton model. A rich structure of exciton–magnon states has been observed in the photoluminescence spectra. We have carried out a spectroscopic study of the optical second harmonic generation in the region of excitonic transitions, which has allowed the contribution of the toroidal moment and the Fano resonance to the observed signals to be revealed.
The interaction of light with spins in a Heisenberg antiferromagnet with a negligibly low magnetic anisotropy as in RbMnF
3
has been theoretically analyzed. In particular, an optical pump–probe ...experiment, where coherent terahertz magnons are excited by short pump laser pulses in the antiferromagnet and are then detected by a probe pulse delayed with respect to the pump pulse, has been simulated. It has been shown that the giant increase in the intensity of excitation of terahertz magnons under the influence of the inverse Cotton–Mouton effect occurs near parametric resonance, i.e., in the parametric instability region.
The goal of this work is to study the processes of self-organization in tetraphenylporphyrin (H
2
TPP) films made by condensation under various conditions. Experimental studies of the spectral ...characteristics of H
2
TPP thin films obtained by the liquid method from a H
2
TPP toluene solution and by vacuum deposition on different substrates are carried out. It is shown that the structure of the H
2
TPP samples changes depending on the technique of synthesis on different substrates, which shows itself in changes (“red” shift) in the photoluminescence and absorption spectra. The changes are caused by a different degree of crystallinity depending on the homogeneity of the surface of the substrates and their temperature.
Controlled generation of coherent spin waves with highest possible frequencies and shortest possible wavelengths is a cornerstone of spintronics and magnonics. Here, using Heisenberg antiferromagnet ...RbMnF3, we demonstrate that laser-induced THz spin dynamics corresponding to pairs of mutually coherent counter-propagating spin waves with the wavevectors up to the edge of the Brillouin zone cannot be understood in terms of magnetization and antiferromagnetic (Néel) vectors, conventionally used to describe spin waves. Instead, we propose to model such spin dynamics using the spin correlation function. We derive a quantum-mechanical equation of motion for the latter and emphasize that unlike the magnetization and antiferromagnetic vectors the spin correlations in antiferromagnets do not exhibit inertia.
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