arXiv subjects

Vitalyi E. Gusev

Publications and source records attributed to Vitalyi E. Gusev.

12 recordsLinked to original sources

arXiv2025

Efficient launch of shear phonons in photostrictive halide perovskites

Optical generation of transverse coherent phonons by femtosecond light pulses is appealing for high-speed sub-THz active control of material properties. Lead-free double perovskite semiconductors, such as Cs2AgBiBr6, attract particular interest due to their cubic to tetragonal phase transition below room temperature and strong polaron effects from carrier-lattice coupling. Here, we reveal that the anisotropic photostriction in halide perovskites with tetragonal crystal structure represents an efficient non-thermal tool for generating transverse coherent phonons. In particular, we demonstrate that along with compressive strain, optical generation of photoexcited carriers leads to strong shear strain in Cs2AgBiBr6 below the phase transition temperature of 122 K. Using time-domain Brillouin spectroscopy, we observe coherent transverse and longitudinal acoustic phonons with comparable amplitudes in the tetragonal phase, while in the cubic phase only longitudinal phonons are generated. The polarization of the photoinduced transverse phonons is dictated by the projection of the c-axis on the surface plane, which leads to a prominent anisotropic polarization response in the detection. The generated strain pulses correspond to transverse acoustic soft eigenmodes with a strong temperature dependence of dispersion, which provides an additional degree of freedom for active hypersonic control.

cond-mat.mtrl-sci↗

arXiv2024

Optically-Controlled Nano-Transducers Based on Cleaved Superlattices for Monitoring Gigahertz Surface Acoustic Vibrations

Surface acoustic waves (SAWs) convey energy at subwavelength depths along surfaces. Using interdigital transducers (IDTs) and opto-acousto-optic transducers (OAOTs), researchers have harnessed coherent SAWs with nanosecond periods and micrometer localization depth for various applications. However, the utilization of cutting-edge OAOTs produced through surface nanopatterning techniques has set the upper limit for coherent SAW frequencies below 100 GHz, constrained by factors such as the quality and pitch of the surface nanopattern, not to mention the electronic bandwidth limitations of the IDTs. In this context, unconventional optically-controlled nano-transducers based on cleaved superlattices (SLs) are here presented as an alternative solution. To demonstrate their viability, we conducted proof-of-concept experiments using ultrafast lasers in a pump-probe configuration on SLs made of alternating AlxGa1-xAs and AlyGa1-yAs layers with approximately 70 nm periodicity and cleaved along their growth direction to produce a periodic nanostructured surface. The acoustic vibrations, generated and detected by laser beams incident on the cleaved surface, span a range from 40 GHz to 70 GHz, corresponding to the generalized surface Rayleigh mode and bulk modes within the dispersion relation. This exploration shows that, in addition to SAWs, cleaved SLs offer the potential to observe surface-skimming longitudinal and transverse acoustic waves at GHz frequencies. This proof-of-concept demonstration below 100 GHz in nanoacoustics using such an unconventional platform offers opportunities for realizing sub-THz to THz coherent surface acoustic vibrations in the future, as SLs can be epitaxially grown with atomic-scale layer width and quality.

physics.optics↗

arXiv2023

Time-domain Brillouin scattering theory for probe light and acoustic beams propagating at an angle and acousto-optic interaction at material interfaces

A theory has been developed to interpret time-domain Brillouin scattering (TDBS) experiments involving coherent acoustic pulse (CAP) and light pulse beams propagating at an angle to each other. It predicts the influence of the directivity pattern of their acousto-optic interaction on TDBS signals when heterodyne detection of acoustically scattered light is in backward direction to incident light. The theory reveals the relationships between the carrier frequency, amplitude and duration of acoustically induced "wave packets" in light transient reflectivity signals, and factors such as CAP duration, widths of light and sound beams, and their interaction angle. It describes the transient dynamics of these wave packets when the light and CAP encounter material interfaces, and the light scattering by the incident CAP transforms into scattering by the reflected and transmitted CAPs. The theory suggests that single-point TDBS experiments can determine not only the depth positions of buried interfaces but also their inclinations/orientations.

cond-mat.mtrl-sci↗

arXiv2022

Ballistic Dynamics of Flexural Thermal Movements in a Nano-membrane Revealed with Subatomic Resolution

Flexural oscillations of free-standing films, nano-membranes and nano-wires are attracting growing attention for their importance to the thermal, electrical and mechanical properties of 2D materials. Here we report on the observation of short-timescale ballistic motion in the flexural mode of a nano-membrane cantilever, driven by thermal fluctuation of flexural phonons, including measurements of ballistic velocities and displacements performed with sub-atomic resolution, using a new free electron edge-scattering technique. Within intervals <10 μs, the membrane moves ballistically at a constant velocity, typically ~300 μm/s, while Brownian-like dynamics emerge for longer observation periods. Access to the ballistic regime provides verification of the equipartition theorem and Maxwell-Boltzmann statistics for flexural modes, and can be used in fast thermometry and mass sensing during atomic absorption/desorption processes on the membrane. We argue that the ballistic regime should be accounted for in understanding the electrical, optical, thermal and mechanical properties of 2D materials.

cond-mat.stat-mech↗

arXiv2021

Protected Long-Distance Guiding of Hypersound Underneath a Nano-Corrugated Surface

Within a new paradigm for communications on the nanoscale, high-frequency surface acoustic waves are becoming effective data carrier and encoder. On-chip communications require acoustic wave propagation along nano-corrugated surfaces which strongly scatter traditional Rayleigh waves. Here we propose the delivery of information using subsurface acoustic waves with hypersound frequencies ~20 GHz, which is a nanoscale analogue of subsurface sound waves in the ocean. A bunch of subsurface hypersound modes is generated by pulsed optical excitation in a multilayer semiconductor structure with a metallic nanograting on top. The guided hypersound modes propagate coherently beneath the nanograting, retaining the surface imprinted information, on a distance of more than 50 μm which essentially exceeds the propagation length of Rayleigh waves. The concept is suitable for interfacing single photon emitters, such as buried quantum dots, carrying coherent spin excitations in magnonic devices, and encoding the signals for optical communications at the nanoscale.

cond-mat.mes-hall↗

arXiv2020

3D characterisation of individual grains of coexisting high-pressure H2O ice phases by time-domain Brillouin scattering

Time-domain Brillouin scattering uses ultrashort laser pulses to generate coherent acoustic pulses of picoseconds duration in a solid sample and to follow their propagation in order to image material inhomogeneities with sub-optical depth resolution. The width of the acoustic pulse limits the spatial resolution of the technique along the direction of the pulse propagation to less than several tens of nanometres. Thus, the time-domain Brillouin scattering outperforms axial resolution of the classical frequency-domain Brillouin scattering microscopy, which uses continuous lasers and thermal phonons and which spatial resolution is controlled by light focusing. The technique benefits from the application of the coherent acoustic phonons, and its application has exciting perspectives for the nanoscale imaging in biomedical and material sciences. In this study, we report on the application of the time-domain Brillouin scattering to the 3D imaging of a polycrystal of water ice containing two high-pressure phases. The imaging, accomplished via a simultaneous detection of quasi-longitudinal and quasi-shear waves, provided the opportunity to identify the phase for individual grains and evaluate their crystallographic orientation. Monitoring the propagation of the acoustic waves in two neighbouring grains simultaneously provided an additional mean for the localisation of the grain boundaries.

cond-mat.mtrl-sci↗

arXiv2020

Contra-Intuitive Features of Time-Domain Brillouin Scattering in Collinear Paraxial Sound and Light Beams

Time-domain Brillouin scattering is an opto-acousto-optical probe technique for the evaluation of the transparent materials. Ultrashort pump laser pulses via optoacoustic conversion launch in the sample picosecond coherent acoustic pulses. The time-delayed ultrashort probe laser pulses monitor the propagation of the coherent acoustic pulses via photo-elastic effect, which induces light scattering. A photodetector collects acoustically scattered light and the probe light reflected by the sample structure for the heterodyning. The scattered probe light carriers the information on the acoustical, optical and acousto-optical parameters of the material in the current position of the coherent acoustic pulse. Thus, among other applications, the time-domain Brillouin scattering is a technique for three-dimensional imaging. Sharp focusing of the coherent acoustic pulses and probe laser pulses could increase lateral spatial resolution of imaging, but could potentially diminish the depth of imaging. However, the theoretical analysis presented in this manuscript contra-intuitively demonstrates that the depth and spectral resolution of the time-domain Brillouin scattering imaging, with collinearly propagating paraxial sound and light beams, do not depend at all on the focusing/diffraction of sound. The variations of the amplitude of the time-domain Brillouin scattering signal are only due to the variations of the probe light amplitude caused by light focusing/diffraction. Although the amplitude of the acoustically scattered light is proportional to the product of the local acoustical and probe light field amplitudes the temporal dynamics of the time-domain Brillouin scattering signal amplitude is independent of the dynamics of the coherent acoustic pulse amplitude.

physics.app-ph↗

arXiv2020

Resonant thermal energy transfer to magnons in a ferromagnetic nanolayer

Energy harvesting is a modern concept which makes dissipated heat useful by transferring thermal energy to other excitations. Most of the existing principles for energy harvesting are realized in systems which are heated continuously, for example generating DC voltage in thermoelectric devices. Here we present the concept of high-frequency energy harvesting where the dissipated heat in a sample excites resonant magnons in a 5-nm thick ferromagnetic metal layer. The sample is excited by femtosecond laser pulses with a repetition rate of 10 GHz which results in temperature modulation at the same frequency with amplitude ~0.1 K. The alternating temperature excites magnons in the ferromagnetic nanolayer which are detected by measuring the net magnetization precession. When the magnon frequency is brought onto resonance with the optical excitation, a 12-fold increase of the amplitude of precession indicates efficient resonant heat transfer from the lattice to coherent magnons. The demonstrated principle may be used for energy harvesting in various nanodevices operating at GHz and sub-THz frequency ranges.

cond-mat.mtrl-sci↗

arXiv2018

On the magnetoelastic and magnetoelectric couplings across the antiferromagnetic transition in multiferroic BiFeO3

Clear anomalies in the lattice thermal expansion (deviation from linear variation) and elastic properties (softening of the sound velocity) at the antiferromagnetic-to-paramagnetic transition are observed in the prototypical multiferroic BiFeO3 using a combination of picosecond acoustic pump-probe and high-temperature X-ray diffraction experiments. Similar anomalies are also evidenced using first-principles calculations supporting our experimental findings. Those calculations in addition to a simple Landau-like model we also developed allow to understand the elastic softening and lattice change at T_N as a result of magnetostriction combined with electrostrictive and magnetoelectric couplings which renormalize the elastic constants of the high-temperature reference phase when the critical T_N temperature is reached.

cond-mat.mtrl-sci↗

arXiv2018

Advances in applications of time-domain Brillouin scattering for nanoscale imaging

Time-domain Brillouin scattering is an all-optical experimental technique based on ultrafast lasers applied for generation and detection of coherent acoustic pulses on time durations of picoseconds and length scales of nanometers. In transparent materials scattering of the probe laser beam by the coherent phonons permits imaging of sample inhomogeneity. The transient optical reflectivity of the sample recorded by the probe beam as the acoustic nanopulse propagates in space contains information on the acoustical, optical, and acousto-optical parameters of the material under study. The experimental method is based on a heterodyning where weak light pulses scattered by the coherent acoustic phonons interfere at the photodetector with probe light pulses of significantly higher amplitude reflected from various interfaces of the sample. The time-domain Brillouin scattering imaging is based on Brillouin scattering and has the potential to provide all the information that researchers in material science, physics, chemistry, biology etc., get with classic frequency-domain Brillouin scattering of light. It can be viewed as a replacement for Brillouin scattering and Brillouin microscopy in all investigations where nanoscale spatial resolution is either required or advantageous. Here we review applications of time-domain Brillouin scattering for imaging of nanoporous films, ion-implanted semiconductors and dielectrics, texture in polycrystalline materials and inside vegetable and animal cells, and for monitoring the transformation of nanosound caused by nonlinearity and focusing. We also discuss the perspectives and the challenges for the future.

physics.app-ph↗

arXiv2014

Revealing sub-μm inhomogeneities and μm-scale texture in H2O ice at Megabar pressures via sound velocity measurements by time-domain Brillouin scattering

Time-domain Brillouin scattering technique, also known as picosecond ultrasonic interferometry, which provides opportunity to monitor propagation of nanometers to sub-micrometers length coherent acoustic pulses in the samples of sub-micrometers to tens of micrometers dimensions, was applied to depth-profiling of polycrystalline aggregate of ice compressed in a diamond anvil cell to Megabar pressures. The technique allowed examination of characteristic dimensions of elastic inhomogeneities and texturing of polycrystalline ice in the direction normal to the diamond anvil surfaces with sub-micrometer spatial resolution via time-resolved measurements of variations in the propagation velocity of the acoustic pulse traveling in the compressed sample. The achieved two-dimensional imaging of the polycrystalline ice aggregate in-depth and in one of the lateral directions indicates the feasibility of three-dimensional imaging and quantitative characterization of acoustical, optical and acousto-optical properties of transparent polycrystalline aggregates in diamond anvil cell with tens of nanometers in-depth resolution and lateral spatial resolution controlled by pump laser pulses focusing.

cond-mat.mtrl-sci↗

arXiv2014

Nonlinear Acoustics at GHz Frequencies in a Viscoelastic Fragile Glass Former

Using a picosecond pump-probe ultrasonic technique, we study the propagation of high-amplitude, laser-generated longitudinal coherent acoustic pulses in the viscoelastic fragile glass former DC704. We observe an increase of almost ten percent in acoustic pulse propagation speed of its leading shock front at the highest optical pump fluence which is a result of the supersonic nature of nonlinear propagation in the viscous medium. From our measurement we deduce the nonlinear acoustic parameter of the glass former in the GHz frequency range across the glass transition temperature.

cond-mat.mtrl-sci↗