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A. V. Frolov

Publications and source records attributed to A. V. Frolov.

12 recordsLinked to original sources
arXiv2024

Identification of a replicable optical security element using laser speckle

An optical security element containing an area of random rough relief is proposed. It combines the low cost of mass replication inherent in traditional security holograms with the impossibility of holographic copying, when the wave restored by the hologram is rewritten as a copy of this hologram. The proposed optical element is also protected from contact and photographic copying. Laboratory samples of optical elements were obtained by taking replicas of a rough surface. Identification of the authenticity of optical elements was demonstrated by calculating the cross-correlation of speckle patterns produced by coherent light scattered off different replicas. It is assumed that the proposed security elements can be mass-produced on standard equipment for embossing security holograms.

cs.CR↗
arXiv2024

Comparative study of magnetic quantum oscillations in Hall and transverse magnetoresistance

Magnetic quantum oscillations (MQO) of Hall coefficient are measured in rare-earth tritelluride TmTe$_{3}$ and shown to be much stronger and persist to higher temperature than the Shubnikov oscillations. It is general for MQO in strongly anisotropic metals, and the combined measurements of Hall and diagonal magnetoresistance provide useful informations about the electronic structure. The ratio of their MQO amplitudes depends linearly on magnetic field, and its slope gives a simple and accurate measurement tool of the electron mean free time and its temperature dependence.

cond-mat.str-el↗
arXiv2023

Inhomogeneous superconductivity onset in FeSe studied by transport properties

Heterogeneous superconductivity onset is a common phenomenon in high-$T_c$ superconductors of both the cuprate and iron-based families. It is manifested by a fairly wide transition from the metallic to zero-resistance state. Usually, in these strongly anisotropic materials, superconductivity (SC) first appears as isolated domains. This leads to anisotropic excess conductivity above $T_c$, and the transport measurements provide valuable information about the SC domain structure deep within the sample. In bulk samples, this anisotropic SC onset gives an approximate average shape of SC grains, while in thin samples it also indicates the average size of SC grains. In this work, both interlayer and intralayer resistivity are measured as a function of temperature in FeSe samples of various thickness. To measure the interlayer resistivity, FeSe mesa structures oriented across the layers were fabricated using FIB. As the sample thickness decreases, a significant increase in superconducting transition temperature $T_c$ is observed : $T_c$ raises from 8 K in bulk material to 12 K in microbridges of thickness $\sim 40$ nm. We apply analytical and numerical calculations to analyze these and earlier data and find the aspect ratio and size of the SC domains in FeSe consistent with our resistivity and diamagnetic response measurements. We propose a simple and fairly accurate method for estimating the aspect ratio of SC domains from $T_c$ anisotropy in samples of various small thickness. The relationship between nematic and superconducting domains in FeSe is discussed. We also generalize the analytical formulas for conductivity in heterogeneous anisotropic superconductors to the case of elongated SC domains of two perpendicular orientations with equal volume fractions, corresponding to the nematic domain structure in various Fe-based superconductors.

cond-mat.supr-con↗
arXiv2020

Toward equilibrium ground state of charge density waves in rare-earth tritellurides

We show that the charge density wave (CDW) ground state below the Peierls transition temperature, $T_{CDW}$, of rare-earth tritellurides is not at its equilibrium value, but depends on the time where the system was kept at a fixed temperature below $T_{CDW}$. This ergodicity breaking is revealed by the increase of the threshold electric field for CDW sliding which depends exponentially on time. We tentatively explain this behavior by the reorganization of the oligomeric (Te$_x$)$^{2-}$ sequence forming the CDW modulation.

cond-mat.str-el↗
arXiv2019

Charge density wave sliding driven by an interplay of conventional and Hall voltages in NbSe$_3$ microbridges

Collective charge-density wave (CDW) transport was measured under a high magnetic field in NbSe$_3$ microbridges which have been cut transversely and at an angle to the chains' direction. We give evidences that the CDW sliding is driven by the Hall voltage generated by the inter-chain current of normal carriers. We have discovered a re-entrance effect of the Hall-driven sliding above a crossover temperature at which the Hall constant has been known to change sign. For the narrow channel, cut at 45$^\circ$ relative to the chain axis, we observed an evolution from the Hall-driven sliding at low temperatures, to the conventional sliding at higher temperatures, which corroborates with falling of the Hall constant. In this course, the nonlinear contribution to the conductivity coming from the collective sliding changes sign. The quantization of Shapiro-steps, generated presumably by a coherent sequence of phase slips, indicates that their governing changes from the applied voltage to the current.

cond-mat.str-el↗
arXiv2019

Anisotropic ultrafast optical response of terahertz pumped graphene

We have measured the ultrafast anisotropic optical response of highly doped graphene to an intense single cycle terahertz pulse. The time profile of the terahertz-induced anisotropy signal at 800 nm has minima and maxima repeating those of the pump terahertz electric field modulus. It grows with increasing carrier density and demonstrates a specific nonlinear dependence on the electric field strength. To describe the signal, we have developed a theoretical model that is based on the energy and momentum balance equations and takes into account optical phonons of graphene and substrate. According to the theory, the anisotropic response is caused by the displacement of the electronic momentum distribution from zero momentum induced by the pump electric field in combination with polarization dependence of the matrix elements of interband optical transitions.

cond-mat.mes-hall↗
arXiv2019

Ti2NiCu Based Composite Nanotweezers with a Shape Memory Effect and its Use for DNA Bunches 3D Manipulation

The DNA molecules were controllable deposited on graphene and thin graphite films and visualized using AFM. The mechanical micro- and nanotools, such as nanotweezers with shape memory effect controlled by heating were designed and tested. A technique for fabricating a structure with the inclusion of suspended DNA threads and manipulating those using composite nanotweezers with shape memory effect was suggested.

physics.bio-ph↗
arXiv2016

Gossamer bulk high-temperature superconductivity in FeSe

The cuprates and iron-based high-temperature superconductors share many common features: layered strongly anisotropic crystal structure, strong electronic correlations, interplay between different types of electronic ordering, the intrinsic spatial inhomogeneity due to doping. The understanding of complex interplay between these factors is crucial for a directed search of new high-temperature superconductors. Here we show the appearance of inhomogeneous gossamer superconductivity in bulk FeSe compound at ambient pressure and at temperature 5 times higher than its zero-resistance $T_c$. This discovery helps to understand numerous remarkable superconducting properties of FeSe. We also find and prove a general property: if inhomogeneous superconductivity in a anisotropic conductor first appears in the form of isolated superconducting islands, it reduces electric resistivity anisotropically with maximal effect along the least conducting axis. This gives a simple and very general tool to detect inhomogeneous superconductivity in anisotropic compounds, which is critically important to study the onset of high-temperature superconductivity.

cond-mat.supr-con↗
arXiv2015

Proximity Effect in Periodic Arrays of Superconducting Nanoislands on Thin Graphite Layer

The regular structure of superconducting nanoislands of alloy W-Ga-C was fabricated on nanothin graphite using focused ion beam. The resistance vs temperature dependence down to 1.7K and the magnetoresistance in field up to 24T were measured both for the bridge containing nanoislands and for the reference bridge without islands. The difference between those measurements demonstrates the proximity effect on a regular structure of superconducting W-Ga-C nanoislands on nanothin graphite layer.

cond-mat.mes-hall↗
arXiv2015

Orbital Quantization in a System of Edge Dirac Fermions in Nanoperforated Graphene

The dependence of the electric resistance R of nanoperforated graphene samples on the position of the Fermi level, which is varied by the gate voltage Vg, has been studied. Nanoperforation has been performed by irradiating graphene samples on a Si/SiO$_2$ substrate by heavy (xenon) or light (helium) ions. A series of regular peaks have been revealed on the R(Vg) dependence at low temperatures in zero magnetic field. These peaks are attributed to the passage of the Fermi level through an equidistant ladder of levels formed by orbitally quantized states of edge Dirac fermions rotating around each nanohole. The results are in agreement with the theory of edge states for massless Dirac fermions.

cond-mat.mes-hall↗
arXiv2009

Non-Gaussianity as a Probe of the Physics of the Primordial Universe and the Astrophysics of the Low Redshift Universe

A new and powerful probe of the origin and evolution of structures in the Universe has emerged and been actively developed over the last decade. In the coming decade, non-Gaussianity, i.e., the study of non-Gaussian contributions to the correlations of cosmological fluctuations, will become an important probe of both the early and the late Universe. Specifically, it will play a leading role in furthering our understanding of two fundamental aspects of cosmology and astrophysics: (i) the physics of the very early universe that created the primordial seeds for large-scale structures, and (ii) the subsequent growth of structures via gravitational instability and gas physics at later times. To date, observations of fluctuations in the Cosmic Microwave Background (CMB) and the Large-Scale Structure of the Universe (LSS) have focused largely on the Gaussian contribution as measured by the two-point correlations (or the power spectrum) of density fluctuations. However, an even greater amount of information is contained in non-Gaussianity and a large discovery space therefore still remains to be explored. Many observational probes can be used to measure non-Gaussianity, including CMB, LSS, gravitational lensing, Lyman-alpha forest, 21-cm fluctuations, and the abundance of rare objects such as clusters of galaxies and high-redshift galaxies. Not only does the study of non-Gaussianity maximize the science return from a plethora of present and future cosmological experiments and observations, but it also carries great potential for important discoveries in the coming decade.

astro-ph.CO↗