arXiv subjects

V. V. Baranov

Publications and source records attributed to V. V. Baranov.

8 recordsLinked to original sources

arXiv2024

The effect of cerium doping and rate of crystallization on the microstructure of the Al2O3/YAG eutectic composite

Eutectics of Sapphire/Yttrium-Aluminum garnet and Ce-doped Sapphire/Yttrium-Aluminum garnet (Ce up to 1 at.%) with a Chinese script microstructure were obtained by the method of horizontal directional crystallization in a carbon-containing reducing atmosphere based on argon gas. The effects of the pooling rate and Ce-dopant concentration on the microstructure of the eutectic were studied by the modified chord method. The deviation of the dependence of the characteristic eutectic distance on the pooling rate from the Jackson-Hunt model has been established. A change in the pathway for restructuring the structure of the doped eutectic at a certain critical pooling rate was revealed, which may indicate that the development of morphological instability of the crystallization front is carried out as a two-stage process. The conditions for obtaining doped eutectic of high homogeneity have been established. It was shown that increasing cerium ion concentration causes an increase in the structure parameters and its value deviation. Intensive formation of the third phase occurred when the limit of cerium ion concentration was exceeded.

cond-mat.mtrl-sci↗

arXiv2017

Dynamics of the superconducting order parameter through ultrafast normal-to-superconducting phase transition in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ from multi-pulse polarization-resolved transient optical reflectivity

A systematic temperature dependent study of the femtosecond optical superconducting (SC) state destruction and recovery in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ cuprate superconductor by means of the all-optical polarization-sensitive multi-pulse spectroscopy is presented. At low temperatures and a partial SC state suppression an anisotropic SC-gap recovery-timescale is suggested by the data. The SC state destruction and recovery dynamics are compared to the recent TR-ARPES-inferred SC-gap dynamics and a qualitative agreement is found. Using a phenomenological response function the experimental data are also compared to time dependent Ginzburg-Landau model simulations.

cond-mat.supr-con↗

arXiv2016

Upper critical field in the model with finite range interaction between electrons

We develop a theory of the upper critical field in a BCS superconductor with a nonlocal interaction between electrons. We have shown that the nonlocal interaction is characterized by the parameter $k_Fρ_0$ where $k_F$ is the Fermi momentum and $ρ_0$ is the radius of electron-electron interaction. The presence of the external magnetic field leads to the generation of additional components of the order parameter with different angular momentum. This effect leads to the enhancement of the upper critical field above the orbital limiting field. In addition the upward curvature in the temperature dependence of $H_{c2}(T)$ in the clean limit is predicted. The impurity scattering suppresses the effect in the dirty limit.

cond-mat.supr-con↗

arXiv2016

Real time measurement of the emergence of superconducting order in a high temperature superconductor

Systems which rapidly evolve through symmetry-breaking transitions on timescales comparable to the fluctuation timescale of the single-particle excitations may behave very differently than under controlled near-ergodic conditions. A real-time investigation with high temporal resolution may reveal new insights into the ordering through the transition that are not available in static experiments. We present an investigation of the system trajectory through a normal-to-superconductor transition in a prototype high-temperature superconducting cuprate in which such a situation occurs. Using a multiple pulse femtosecond spectroscopy technique we measure the system trajectory and time-evolution of the single-particle excitations through the transition in La$_{1.9}$Sr$_{0.1}$CuO$_{4}$ and compare the data to a simulation based on time-dependent Ginzburg-Landau theory, using laser excitation fluence as an adjustable parameter controlling the quench conditions in both experiment and theory. The comparison reveals the presence of significant superconducting fluctuations which precede the transition on short timescales. By including superconducting fluctuations as a seed for the growth of superconducting order we can obtain a satisfactory agreement of the theory with the experiment. Remarkably, the pseudogap excitations apparently play no role in this process.

cond-mat.supr-con↗

arXiv2014

Theory of the electron relaxation in metals excited by an ultrashort optical pump

The theory of the electron relaxation in metals excited by an ultrashort optical pump is developed on the basis of the solution of the linearized kinetic equation. The kinetic equation includes both the electron-electron and the electron-phonon collision integrals. The widely used two temperature model follows from the theory as the limiting case, when the thermalization due to the electronelectron collisions is fast with respect to the electron-phonon relaxation. It is demonstrated that the energy relaxation has two consecutive processes. The first and most important step describes the emission of phonons by the photo-excited electrons. It leads to the relaxation of 90% of the energy before the electrons become thermalized among themselves. The second step describes electronphonon thermalization and may be described by the two temperature model. The second stage is difficult to observe experimentally because it involves the transfer of only a small amount of energy from electrons. Thus the theory explains why the divergence of the relaxation time at low temperatures was never observed experimentally.

cond-mat.str-el↗

arXiv2013

Dynamics of resistive state in thin superconducting channels

We theoretically study how the dynamics of the resistive state in narrow superconducting channels shunted by an external resistor depends on channel's length $L$, the applied current $j$, and parameter $u$ characterizing the penetration depth of the electric field in the nonequilibrium superconductors. We show that changing $u$ dramatically affects both the behaviour of the current-voltage characteristics of the superconducting channels and the dynamics of their order parameter. Previously, it was demonstrated that when $u$ is less than the critical value $u_{c1}$, which does not depend on $L$, the phase slip centers appear simultaneously at different spots of the channel. Herewith, for $u>u_{c1}$ these centres arise consecutively at the same place. In our work we demonstrate that there is another critical value for $u$. Actually, if $u$ does not exceed a certain value $u_{c2}$, which depends on $L$, the current-voltage characteristic exhibits the step-like behaviour. However, for $u>u_{c2}$ it becomes hysteretic. In this case, with increase of $j$ the steady state, which corresponds to the time independent distribution of the order parameter along the channel, losses its stability at switching current value $j_{sw}$, and time periodic oscillations of both the order parameter and electric filed occur in the channel. As $j$ sweeps down, the periodic dynamics ceases at certain retrapping current value $j_r<j_{sw}$. Shunting the channel by a resistor increases the value of $j_r$, while $j_{sw}$ remains unchanged. Thus, for some high enough conductivity of the shunt $j_r$ and $j_{sw}$ eventually coincide, and the hysteretic loop disappears. We reveal dynamical regimes involved in the hysteresis, and discuss the bifurcation transitions between them.

cond-mat.supr-con↗

arXiv2011

The bifurcation phenomena in the resistive state of the narrow superconducting channels

We have investigated the properties of the resistive state of the narrow superconducting channel of the length L/ξ=10.88 on the basis of the time-dependent Ginzburg-Landau model. We have demonstrated that the bifurcation points of the time-dependent Ginzburg-Landau equations cause a number of singularities of the current-voltage characteristic of the channel. We have analytically estimated the averaged voltage and the period of the oscillating solution for the relatively small currents. We have also found the range of currents where the system possesses the chaotic behavior.

cond-mat.supr-con↗

arXiv2011

Current-voltage characteristic of narrow superconducting wires: bifurcation phenomena

The current-voltage characteristics of long and narrow superconducting channels are investigated using the time-dependent Ginzburg-Landau equations for complex order parameter. We found out that the steps in the current voltage characteristic can be associated with bifurcations of either steady or oscillatory solution. We revealed typical instabilities which induced the singularities in current-voltage characteristics, and analytically estimated period of oscillations and average voltage in the vicinity of the critical currents. Our results show that these bifurcations can substantially complicate dynamics of the order parameter and eventually lead to appearance of such phenomena as multistability and chaos. The discussed bifurcation phenomena sheds a light on some recent experimental findings.

cond-mat.supr-con↗