arXiv subjects

Roman V. Pisarev

Publications and source records attributed to Roman V. Pisarev.

6 recordsLinked to original sources

arXiv2023

Impulsive Fermi magnon-phonon resonance in antiferromagnetic $CoF_{2}$

Understanding spin-lattice interactions in antiferromagnets is one of the most fundamental issues at the core of the recently emerging and booming fields of antiferromagnetic spintronics and magnonics. Recently, coherent nonlinear spin-lattice coupling was discovered in an antiferromagnet which opened the possibility to control the nonlinear coupling strength and thus showing a novel pathway to coherently control magnon-phonon dynamics. Here, utilizing intense narrow band terahertz (THz) pulses and tunable magnetic fields up to 7 T, we experimentally realize the conditions of the Fermi magnon-phonon resonance in antiferromagnetic $CoF_{2}$. These conditions imply that both the spin and the lattice anharmonicities harvest energy transfer between the subsystems, if the magnon eigenfrequency $f_{m}$ is twice lower than the frequency of the phonon $2f_{m}=f_{ph}$. 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 an impulsive THz-induced response. This study focuses on the role of nonlinearity in spin-lattice interactions, providing insights into the control of coherent magnon-phonon energy exchange.

cond-mat.mes-hall↗

arXiv2022

The importance of the interface for picosecond spin pumping in antiferromagnet-heavy metal heterostructures

Interfaces between heavy metals (HMs) and antiferromagnetic insulators (AFIs) have recently become highly investigated and debated systems in the effort to create spintronic devices able to function at terahertz frequencies. Such heterostructures have great technological potential because AFIs can generate sub-picosecond spin currents which the HMs can convert into charge signals. In this work we demonstrate an optically induced picosecond spin transfer at the interface between AFIs and Pt using time-resolved THz emission spectroscopy. We select two antiferromagnets in the same family of fluoride cubic perovskites, KCoF3 and KNiF3, whose magnon frequencies at the centre of the Brillouin zone differ by an order of magnitude. By studying their behaviour with temperature we correlate changes in the spin transfer efficiency across the interface to the opening of a gap in the magnon density of states below the Néel temperature. Our observations are reproduced in a model based on the spin exchange between the localized electrons in the antiferromagnet and the free electrons in Pt. These results constitute an important step in the rigorous investigation and understanding of the physics of AFIs/HMs interfaces on the ultrafast timescale.

cond-mat.mes-hall↗

arXiv2021

Terahertz-Light Driven Coupling of Antiferromagnetic Spins to Lattice

Understanding spin-lattice coupling represents a key challenge in modern condensed matter physics, with crucial importance and implications for ultrafast and 2D-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 THz light pulses. A nearly single-cycle THz pulse resonantly interacts with a coherent magnonic state in the antiferromagnet CoF2 and excites the Raman-active THz phonon. The results reveal the unique functionality of antiferromagnets allowing ultrafast spin-lattice coupling using light.

cond-mat.str-el↗

arXiv2018

Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation

To gain control over magnetic order on ultrafast time scales, a fundamental understanding of the way electron spins interact with the surrounding crystal lattice is required. However, measurement and analysis even of basic collective processes such as spin-phonon equilibration have remained challenging. Here, we directly probe the flow of energy and angular momentum in the model insulating ferrimagnet yttrium iron garnet. Following ultrafast resonant lattice excitation, we observe that magnetic order reduces on distinct time scales of 1 ps and 100 ns. Temperature-dependent measurements, a spin-coupling analysis and simulations show that the two dynamics directly reflect two stages of spin-lattice equilibration. On the 1-ps scale, spins and phonons reach quasi-equilibrium in terms of energy through phonon-induced modulation of the exchange interaction. This mechanism leads to identical demagnetization of the ferrimagnet's two spin-sublattices and a novel ferrimagnetic state of increased temperature yet unchanged total magnetization. Finally, on the much slower, 100-ns scale, the excess of spin angular momentum is released to the crystal lattice, resulting in full equilibrium. Our findings are relevant for all insulating ferrimagnets and indicate that spin manipulation by phonons, including the spin Seebeck effect, can be extended to antiferromagnets and into the terahertz frequency range.

cond-mat.mtrl-sci↗

arXiv2018

Excitation of multiple phonon modes in copper metaborate CuB$_2$O$_4$ via non-resonant impulsive stimulated Raman scattering

Excitation of four coherent phonon modes of different symmetries has been realized in copper metaborate CuB$_2$O$_4$ via impulsive stimulated Raman scattering (ISRS). Phonons were detected by monitoring changes in the linear optical birefringence using the balanced-detection (BD) technique. We compare the results of BD-ISRS experiment to the polarized spontaneous Raman scattering spectra. We show that the agreement between the two sets of data obtained by these allied techniques in a wide phonon frequencies range of 4-14 THz can be achieved by rigorously taking into account the symmetry of the phonon modes, and the corresponding excitation and detection selection rules. It is also important to account for the difference between incoherent and coherent phonons in terms of their contributions to the Raman scattering process. This comparative analysis highlights the importance of the ratio between the frequency of a particular mode, and the pump and probe spectral widths. We demonstrate analytically that the pump and probe pulse durations of 90 and 50 fs, respectively, used in our experiments, limit the highest frequency of the excited and detected coherent phonon modes to 12 THz, and define their relative amplitudes.

cond-mat.mtrl-sci↗

arXiv2017

High resolution resonant inelastic EUV scattering from orbital excitations in a Heisenberg antiferromagnet

We report the high resolution resonant inelastic EUV scattering study of quantum Heisenberg antiferromagnet KCoF3. By tuning the EUV photon energy to cobalt M23 edge, a complete set of low energy 3d spin-orbital excitations is revealed. These low-lying electronic excitations are modeled using an extended multiplet-based mean field calculation to identify the roles of lattice and magnetic degrees of freedom in modifying the RIXS spectral lineshape. We have demonstrated that the temperature dependence of RIXS features upon the antiferromagnetic ordering transition enables us to probe the energetics of short-range spin correlations in this material.

cond-mat.mtrl-sci↗