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A. P. Orlov

Publications and source records attributed to A. P. Orlov.

At least 19 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↗
arXiv2022

Spin mixing conductance and spin magnetoresistance of iridate/manganite interface

We present results on experimental studies of spin current, measured under spin pumping at ferromag-netic resonance in wide frequency band 2-20 GHz for SrIrO3/La0.7Sr0.3MnO3 heterostructures fabricated by RF magnetron sputtering at high temperature. The epitaxial growth of the thin film in heterostructure by a cube-on-cube mechanism was confirmed by XRD and TEM analysis. Taking into account the con-tribution of anisotropic magnetoresistance the spin current was estimated as 1/3 of the total response. We show that both real and imaginary parts of spin mixing conductance are valuable for heterostructures with strong spin-orbit interaction in SrIrO3. Imaginary part of spin mixing conductance was estimated by means of shift of ferromagnetic resonance field of La0.7Sr0.3MnO3 layer in heterostructure. The spin mag-netoresistance was evaluated from angular dependencies of magnetoresistance measured in planar Hall configuration. In order to extract the influence of anisotropic magnetoresistance a La0.7Sr0.3MnO3 film was measured as well. The spin Hall angle for heterostructure was found higher than for interface Pt/ La0.7Sr0.3MnO3.

cond-mat.str-el↗
arXiv2020

Magnons Parametric Pumping in Bulk Acoustic Waves Resonator

We report on the experimental observation of excitation and detection of parametric spin waves and spin currents in the bulk acoustic wave resonator. The hybrid resonator consists of ZnO piezoelectric film, yttrium iron garnet (YIG) films on gallium gadolinium garnet substrate, and a heavy metal Pt layer. Shear bulk acoustic waves are electrically excited in the ZnO layer due to piezoeffect at the resonant frequencies of the resonator. The magnetoelastic interaction in the YIG film emerges magnons (spin waves) excitation by acoustic waves either on resonator's eigenfrequencies or the half-value frequencies at supercritical power. We investigate acoustic pumping of magnons at the half-value frequencies and acoustic spin pumping from parametric magnons, using the inverse spin Hall effect in the Pt layer. The constant electric voltage in the Pt layer, depending on the frequency, the magnetic field, and the pump power, was systematically studied. We explain the low threshold obtained (~0.4 mW) by the high efficiency of electric power transmission into the acoustic wave in the resonator.

cond-mat.mes-hall↗
arXiv2020

Magnetoresistance in quasi-one dimensional Weyl semimetal (TaSe$_4$)$_2$I

Magnetic field effect on linear and nonlinear conductivity in a quasi-one-dimensional Weyl semimetal with a charge density wave (CDW) (TaSe$_4$)$_2$I is studied. Longitudinal magnetoresistance in all known regimes of CDW motion (linear conduction, creep, sliding, "Fröhlich superconductivity") is small, positive and do not exceed a fraction of per cent. Similar magnetotransport measurements were performed in samples profiled by focused ion beams is such a way that motion of the CDW in them is accompanied by phase slip of the CDW. In such samples, a peak-like non-parabolic negative magnetoresistance is observed in relatively small magnetic fields $B \lesssim 4$ T in the nonlinear conduction regime in both longitudinal and transverse geometries. Our results differ significantly from ones obtained earlier and raise the question concerning conditions for observing the axion anomaly in Weyl semimetals in the Peierls state.

cond-mat.mtrl-sci↗
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↗
arXiv2020

Evidence of Charge Density Wave transverse pinning by x-ray micro-diffraction

Incommensurate charge density waves (CDW) have the extraordinary ability to display non-Ohmic behavior when submitted to an external field. The mechanism leading to this non trivial dynamics is still not well understood, although recent experimental studies tend to prove that it is due to solitonic transport. Solitons could come from the relaxation of the strained CDW within an elastic-to-plastic transition. However, the nucleation process and the transport of these charged topological objects have never been observed at the local scale until now. In this letter, we use in-situ scanning x-ray micro-diffraction with micrometer resolution of a NbSe$_3$ sample designed to have sliding and non-sliding areas. Direct imaging of the charge density wave deformation is obtained using an analytical approach based on the phase gradient to disentangle the transverse from the longitudinal components over a large surface of a hundred microns size. We show that the CDW dissociates itself from the host lattice in the sliding regime and displays a large transverse deformation, ten times larger than the longitudinal one and strongly dependent on the amplitude and the direction of the applied currents. This deformation continuously extends across the macroscopic sample dimensions, over a distance 10 000 times greater than the CDW wavelength despite the presence of strong defects while remaining strongly pinned by the lateral surfaces. This 2D quantitative study highlights the prominent role of shear effect that should play a significant role in the nucleation of solitons.

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

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

Transport of Massless Dirac Fermions in Non-topological Type Edge States

There are two types of intrinsic surface states in solids. The first type is formed on the surface of topological insulators. Recently, transport of massless Dirac fermions in the band of "topological" states has been demonstrated. States of the second type were predicted by Tamm and Shockley long ago. They do not have a topological background and are therefore strongly dependent on the properties of the surface. We study the problem of the conductivity of Tamm-Shockley edge states through direct transport experiments. Aharonov-Bohm magneto-oscillations of resistance are found on graphene samples that contain a single nanohole. The effect is explained by the conductivity of the massless Dirac fermions in the edge states cycling around the nanohole. The results demonstrate the deep connection between topological and non-topological edge states in 2D systems of massless Dirac fermions.

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↗
arXiv2013

Aharonov-Bohm resistance magneto-oscillations on single-nanohole graphite and graphene structures

Graphene is a stable single atomic layer material exhibiting two-dimensional electron gas of massless Dirac fermions of high mobility. One of the intriguing properties of graphene is a possibility of realization of the Tamm-type edge states. These states differ from the usual surface states caused by defects, impurities and other imperfections at the edge of the system, as well as they differ from the magnetic edge states caused by skipping cyclotron orbits. The Tamm states result from breaking of periodic crystal potential at the edge, they can exist even at zero magnetic field and form a conducting band. Until recently those states have been observed in graphene only by local STM technique and there were no direct experiments on their contribution to transport measurements. Here we present the experiments on Aharonov-Bohm (AB) oscillations of resistance in a single-nanohole graphite and graphene structures, it indicates the presence of conducting edge states cycling around nanohole. An estimation show the penetration depth of the edge states to be as short as about 2 nm. The oscillations persist up to temperature T=115 K and the T-range of their existence increases with a decrease of the nanohole diameter. The proposed mechanism of the AB oscillations based on the resonant intervalley backscattering of the Dirac fermions by the nanohole via the Tamm states. The experimental results are consistent with such a scenario. Our findings show a way towards interference devices operating at high temperatures on the edge states in graphene

cond-mat.mes-hall↗
arXiv2013

Interlayer tunneling spectroscopy of graphite at high magnetic field oriented parallel to the layers

Interlayer tunneling in graphite mesa-type structures is studied at a strong in-plane magnetic field $H$ up to 55 T and low temperature $T=1.4$ K. The tunneling spectrum $dI/dV$ vs. $V$ has a pronounced peak at a finite voltage $V_0$. The peak position $V_0$ increases linearly with $H$. To explain the experiment, we develop a theoretical model of graphite in the crossed electric $E$ and magnetic $H$ fields. When the fields satisfy the resonant condition $E=vH$, where $v$ is the velocity of the two-dimensional Dirac electrons in graphene, the wave functions delocalize and give rise to the peak in the tunneling spectrum observed in the experiment.

cond-mat.mes-hall↗
arXiv2006

Anomalous asymmetry of magnetoresistance in NbSe$_3$ single crystals

A pronounced asymmetry of magnetoresistance with respect to the magnetic field direction is observed for NbSe$_3$ crystals placed in a magnetic field perpendicular to their conducting planes. It is shown that the effect persists in a wide temperature range and manifests itself starting from a certain magnetic induction value $B_0$, which at $T=4.2$ K corresponds to the transition to the quantum limit, i.to the state where the Landay level splitting exceeds the temperature.

cond-mat.str-el↗