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A. V. Bondarenko

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

At least 19 recordsLinked to original sources
arXiv2026

Optics-microwave entanglement and state teleportation mediated by a cavity magnomechanical system

Generating usable output-entanglement in continuous variable systems can serve as a viable resource for improving applications in quantum information science. In this work, we show how to generate steady-state output-entanglement in a two-stage conversion setup between optical and microwave photon which employs resonantly coupled magnetic and mechanical excitations, as proposed in Phys. Rev. Applied 18, 044059 (2022). We show that the entanglement can be maximized for the same set of parameters which optimize the frequency-conversion efficiency, and that it can be leveraged for a teleportation-based state-transfer protocol for coherent input-states with fidelity close to unity. We propose an implementation based on an Yittrium Iron Garnet disk of micrometer scale, and use both simulation results and reasonable estimates to assess the performance under optimized conditions. We find a maximum teleportation fidelity of $0.75$ for the proposed setup.

quant-ph↗
arXiv2021

Spin-wave eigenmodes in direct-write 3D nanovolcanoes

Extending nanostructures into the third dimension has become a major research avenue in modern magnetism, superconductivity and spintronics, because of geometry-, curvature- and topology-induced phenomena. Here, we introduce Co-Fe nanovolcanoes-nanodisks overlaid by nanorings-as purpose-engineered 3D architectures for nanomagnonics, fabricated by focused electron beam induced deposition. We use both perpendicular spin-wave resonance measurements and micromagnetic simulations to demonstrate that the rings encircling the volcano craters harbor the highest-frequency eigenmodes, while the lower-frequency eigenmodes are concentrated within the volcano crater, due to the non-uniformity of the internal magnetic field. By varying the crater diameter, we demonstrate the deliberate tuning of higher-frequency eigenmodes without affecting the lowest-frequency mode. Thereby, the extension of 2D nanodisks into the third dimension allows one to engineer their lowest eigenfrequency by using 3D nanovolcanoes with 30% smaller footprints. The presented nanovolcanoes can be viewed as multi-mode microwave resonators and 3D building blocks for nanomagnonics.

cond-mat.mes-hall↗
arXiv2020

Engineered magnetization and exchange stiffness in direct-write Co-Fe nanoelements

Media with engineered magnetization are essential building blocks in superconductivity, magnetism and magnon spintronics. However, the established thin-film and lithographic techniques insufficiently suit the realization of planar components with on-demand-tailored magnetization in the lateral dimension. Here, we demonstrate the engineering of the magnetic properties of CoFe-based nanodisks fabricated by the mask-less technique of focused electron beam induced deposition (FEBID). The material composition in the nanodisks is tuned \emph{in-situ} via the e-beam waiting time in the FEBID process and their post-growth irradiation with Ga ions. The magnetization $M_s$ and exchange stiffness $A$ of the disks are deduced from perpendicular ferromagnetic resonance measurements. The achieved $M_s$ variation in the broad range from $720$ emu/cm$^3$ to $1430$ emu/cm$^3$ continuously bridges the gap between the $M_s$ values of such widely used magnonic materials as permalloy and CoFeB. The presented approach paves a way towards nanoscale 2D and 3D systems with controllable and space-varied magnetic properties.

cond-mat.mes-hall↗
arXiv2018

Chaotic dynamics in spin-vortex pairs

We report on spin-vortex pair dynamics measured at temperatures low enough to suppress stochastic core motion, thereby uncovering the highly non-linear intrinsic dynamics of the system. Our analysis shows that the decoupling of the two vortex cores is resonant and can be enhanced by dynamic chaos. We detail the regions of the relevant parameter space, in which the various mechanisms of the resonant core-core dynamics are activated. We show that the presence of chaos can reduce the thermally-induced spread in the switching time by up to two orders of magnitude.

cond-mat.mes-hall↗
arXiv2017

Non-existence of (76,30,8,14) strongly regular graph

We prove the non-existence of strongly regular graph with parameters $(76,30,8,14)$. We use Euclidean representation of a strongly regular graph together with a new lower bound on the number of 4-cliques to derive strong structural properties of the graph, and then use these properties to show that the graph cannot exist.

math.CO↗
arXiv2017

Reversible recovery of excess current in $Y(Ho)-Ba-Cu-O$-normal metal point contacts under high voltages

A polarity-dependent reversible change in the current-voltage characteristics between states corresponding to different values of the excess current ${{I}_{exc}}$ is observed for bias voltages of several hundred millivolts in $Ag-ReB{{a}_{2}}C{{u}_{3}}{{O}_{7-x}}$ $\left( Re\text{ }=\text{ }Y,\text{ }Ho \right)$ point contacts in the current-carrying state. The observed effect has a high intensity (right up to a complete suppression or recovery of ${{I}_{exc}}$) and is not accompanied by a noticeable variation of the energy gap or the critical temperature in the point contact region. It is also established that the states with intermediate values of $I_{exc}$ are stable for zero bias voltages across the point contacts, at least up to $110 \ K$. It is assumed that the variation of ${{I}_{exc}}$ and the corresponding modification of IVC are due to the oxygen migration processes induced by the electric field and current, resulting in a local variation of the superconducting parameters in the point-contact region.

cond-mat.supr-con↗
arXiv2017

Excess conduction of YBaCuO point contacts between 100 and 200 K

$YBaCuO-Ag$ pressure point contacts with direct conduction are investigated. The excess (relative to the normal state) conductivity mainly caused by fluctuational pairing of electrons above $T_c$ is measured in the temperature interval 100-200~$K$. The superconductivity above 120~$K$ is found to be of the two-dimensional type. The obtained preliminary results indicate the presence of small amount of an unknown phase with $T'_c\gtrsim 200~K$ in $YBaCuO$.

cond-mat.supr-con↗
arXiv2014

On concentrators and related approximation constants

Pippenger ([Pippenger, 1977]) showed the existence of $(6m,4m,3m,6)$-concentrator for each positive integer $m$ using a probabilistic method. We generalize his approach and prove existence of $(6m,4m,3m,5.05)$-concentrator (which is no longer regular, but has fewer edges). We apply this result to improve the constant of approximation of almost additive set functions by additive set functions from $44.5$ (established in [Kalton, Roberts, 1983]) to $39$. We show a more direct connection of the latter problem to the Whitney type estimate for approximation of continuous functions on a cube in $\mathbb{R}^d$ by linear functions, and improve the estimate of this Whitney constant from $802$ (proved in [Brudnyi, Kalton, 2000]) to $73$.

math.CA↗
arXiv2012

Mesh ratios for best-packing and limits of minimal energy configurations

For $N$-point best-packing configurations $ω_N$ on a compact metric space $(A,ρ)$, we obtain estimates for the mesh-separation ratio $γ(ω_N,A)$, which is the quotient of the covering radius of $ω_N$ relative to $A$ and the minimum pairwise distance between points in $ω_N$. For best-packing configurations $ω_N$ that arise as limits of minimal Riesz $s$-energy configurations as $s\to \infty$, we prove that $γ(ω_N,A)\le 1$ and this bound can be attained even for the sphere. In the particular case when N=5 on $S^2$ with $ρ$ the Euclidean metric, we prove our main result that among the infinitely many 5-point best-packing configurations there is a unique configuration, namely a square-base pyramid $ω_5^*$, that is the limit (as $s\to \infty$) of 5-point $s$-energy minimizing configurations. Moreover, $γ(ω_5^*,S^2)=1$.

math-ph↗
arXiv2012

Minimal $N$-Point Diameters and $f$-Best-Packing Constants in $R^d$

In terms of the minimal $N$-point diameter $D_d(N)$ for $R^d,$ we determine, for a class of continuous real-valued functions $f$ on $[0,+\infty],$ the $N$-point $f$-best-packing constant $\min\{f(\|x-y\|)\, :\, x,y\in \R^d\}$, where the minimum is taken over point sets of cardinality $N.$ We also show that $$ N^{1/d}Δ_d^{-1/d}-2\le D_d(N)\le N^{1/d}Δ_d^{-1/d}, \quad N\ge 2,$$ where $Δ_d$ is the maximal sphere packing density in $\R^d$. Further, we provide asymptotic estimates for the $f$-best-packing constants as $N\to\infty$.

math-ph↗
arXiv2008

Quasi-static and dynamic order-disorder transition in presence of strong pinning

We present the results of an experimental study of vortex dynamics in non-twinned $YBa_2Cu_3O_{6,87}$ crystal. It is found that critical currents $J_c$ and $J_{c,dyn}$, which correspond to the pinning force in the thermal creep and flux flow mode, respectively, non-monotonically vary with the magnetic field. However, the minimum in the $J_{c,dyn}(H)$ dependence is observed in higher fields, compared with the minimum position $H_{OD}$ in the $J_c(H)$ dependence. Considering that the field $H_{OD}$ corresponds to the static order-disorder transition, this difference is explained by partial dynamic ordering of the vortex solid. It is concluded that finite transverse barriers guarantee finite density of transverse displacements of vortex lines $u_t\simeq c_La_0$ suitable for preservation of the disordered state of the moving vortex solid.

cond-mat.supr-con↗
arXiv2008

Order-disorder transition induced by deformation of vortex lines at the twin boundaries in YBa$_2$Cu$_3$O$_{7-δ}$-crystals: test of the Lindemann criteria

We show that rotation of the magnetic field off the plane of twin boundaries (TB's) induces transition of an ordered vortex solid phase to a disordered one. This transition arises due to appearance of transverse deformations of vortex lines near the TB's, $u_{t,TB}$, the amplitude of which satisfies the Lindemann criteria, $u_{t,rp}=c_La_0$. This order-disorder transition is accompanied by an increase in the depinning current, by crossover from an elastic creep to plastic one, and by appearance of the $S$-shaped voltage-current characteristics.

cond-mat.supr-con↗
arXiv2008

Pinning and Dynamics of Magnetic Flux Moving Across the Twin Planes in YBa_2Cu_3O_6.97 Single Crystal

We present the transport studies of field variation of the pinning force for the flux motion across the twin boundaries in YBaCuO single crystals. It is found that the depinning current J_c decreases with an increase in the magnetic field due to reduction of the portion of vortex lines trapped by the TB's. However, at transport currents J << J_c, the vortex velocity weakly decreases with the increased field, i.e. it is determined mainly by the release of the vortex lines from the TB's.

cond-mat.supr-con↗
arXiv2004

Possible Josephson-like behavior of the YBa2Cu3O7-x single crystal twin boundaries in low magnetic fields

The experimental results on the magnetic response of YBCO single crystals with unidirectional twin boundary planes in low magnetic fields (0.01 - 1 Oe) are discussed. The observed non-monotone temperature dependence of magnetization is interpreted within a plausible model of a system of the Josephson weak links in the twin boundary planes and on the basis of the order parameter anisotropy.

cond-mat.supr-con↗
arXiv2003

Magnetoresistive study of antiferromagnetic--weak ferromagnetic transition in single-crystal La$_{2}$CuO$_{4+δ}$

The resistive measurements were made to study the magnetic field-induced antiferromagnetic (AF) - weak ferromagnetic (WF) transition in La$_2$CuO$_4$ single-crystal. The magnetic field (DC or pulsed) was applied normally to the CuO$_2$ layers. The transition manifested itself in a drastic decrease of the resistance in critical fields of ~5-7 T. The study is the first to display the effect of the AF -WF transition on the conductivity of the La$_2$CuO$_4$ single-crystal in the parallel - to - CuO$_2$ layers direction. The results provide support for the 3-dimensional nature of the hopping conduction of this layered oxide.

cond-mat.str-el↗
arXiv2003

Direct Demonstration of the Anisotropic Origin of the Macroturbulent Instability in Type-II Superconductors

The physical nature of the macroturbulence in the vortex matter in YBCO superconductors is verified by means of magnetooptic study of the instability in a single crystal prepared specially for this purpose. The instability develops near those sample edges where the oppositely directed flow of vortices and antivortices, guided by twin boundaries, is characterized by the discontinuity of the tangential component of the hydrodynamic velocity. This fact directly indicates that the macroturbulence is analogous to the instability of fluid flow at a surface of a tangential velocity discontinuity in classical hydrodynamics, and is related to the anisotropic flux motion in the superconductor.

cond-mat.supr-con↗