arXiv subjects

P. P. Syrnikov

Publications and source records attributed to P. P. Syrnikov.

4 recordsLinked to original sources

arXiv2026

Role of magnon-magnon interaction in optical excitation of coherent two-magnon modes

Two-magnon modes are terahertz-frequency magnetic excitations in antiferromagnets, governed by exchange interactions, involving magnons from the entire Brillouin zone and dominated by zone-edge magnons. The ability to couple to light promotes two-magnon modes as contenders for ultrafast optical manipulation of the magnetic state, beyond conventional zone-center magnonics. While magnon-magnon interactions are known to critically shape the two-magnon line in spontaneous Raman scattering spectra, their role in coherent time-domain excitations remains unexplored. We report a detailed experimental and theoretical study of the influence of magnon-magnon interactions on coherent two-magnon modes in a cubic antiferromagnet excited via Impulsive Stimulated Raman scattering. We reveal the nontrivial evolution of coherent magnetic dynamics in the time domain and the corresponding spectrum and compare it with the spontaneous Raman scattering spectrum. By extending the spin-correlations based theory for two-magnon modes, we derive a unified description of their spectra in Raman Scattering and Impulsive Stimulated Raman Scattering and highlight the role of magnon-magnon interactions.

cond-mat.mtrl-sci↗

arXiv2023

Coherent THz Spin Dynamics in Antiferromagnets Beyond the Approximation of the Néel vector

Controlled generation of coherent spin waves with highest possible frequencies and the shortest possible wavelengths is a cornerstone of spintronics and magnonics. Here, using the Heisenberg antiferromagnet RbMF$_3$, 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.

cond-mat.str-el↗

arXiv2011

Experimental manifestations of the Nb^{4+}-O^{-} polaronic excitons in KTa_{0.988}Nb_{0.012}O_{3}

The formation of the photo-polaronic excitons in ABO_{3} perovskite type oxides has been detected experimentally by means of the photoinduced electron paramagnetic resonance studies of KTa_{0.998}Nb_{0.012}O_{3} crystals. The corresponding microwave X-band spectrum at T < 10 K consists of a narrow, nearly isotropic signal located at g ~ 2 and a strongly anisotropic component. The first signal, which has a rich structure due to hyperfine interactions with the lattice nuclei, is attributed to the single trapped charge carriers: the electrons and/or the holes. The anisotropic spectrum is caused by the axial centers oriented along the C_{4} pseudo-cubic principal crystalline axes. The spectrum angular dependence can be described well by an axial center with S = 1, g_{\parallel) = 0.82, g_{\perp} = 0.52 and D = 0.44 cm^{-1}. The anisotropic spectrum is attributed to the Nb^{4+}-O^{-} polaronic excitons. The temperature dependence of the anisotropic component is characterized by two activation energies: the internal dynamics activation E_{a1} = 3.7\pm0.5 meV, which makes the EPR spectrum unobservable above 10 K, and the destruction energy E_{a2} = 52\pm4 meV. By comparing the anisotropic photo-EPR spectrum and the photoinduced optical absorption temperature dependencies, we found that the Nb^{4+}-O^{-} polaronic excitons also manifested themselves via the ~0.7 eV wide absorption band arising under UV light excitation in the weakly concentrated KTaO_{3}:Nb crystals.

cond-mat.mtrl-sci↗

arXiv2006

Li Doping Effect on Properties and Phase Transfomations of Knbo3

Dielectric permittivity and infrared reflectivity spectra of Li doped KNbO3 single crystals have been studied for the first time for K1-xLixNbO3 (KLN) with x = 0.015, 0.02, 0.065. It was found that like in KTaO3, Li admixture results in appearance of dielectric relaxation with the relaxation parameters very close to those in KTaO3 quantum paraelectric. It was attributed to 90-grad dipole reorientation of Li+ <100> off centers substituted K+, which appear to be presents as in paraelectric cubic phase as in ferroelectric phase down to low temperatures. Besides, Li doping is accompanied by increasing of the cubic-tetragonal phase transition point, decreasing of tetragonal-orthorhombic-rhombohedral phase transition points and TO soft mode stiffen at room temperature.

cond-mat.other↗