arXiv subjects

Y. Kopelevich

Publications and source records attributed to Y. Kopelevich.

41 records · Page 3Linked to original sources

arXiv2001

Nonmonotonic Temperature Dependence of the Thermal Hall Angle of a YBa$_{2}$Cu$_{3}$O$_{6.95}$ Single Crystal

We have performed high-resolution measurements of the magnetic field (0~T~$ \le B \le 9~$T) and temperature (10 K~$\le T < 140~$K) dependence of the longitudinal and transverse Hall thermal conductivity of a twinned YBa$_{2}$Cu$_{3}$O$_{6.95}$ single crystal. We have used and compared two recently published methods to extract the thermal Hall angle $θ_H(T,B)$. Our results indicate that $\cot(θ_H)$ varies quite accurately as $T^4$ in the intermediate temperature range $\sim 0.3 < T/T_c$. It shows a well defined minimum at $T_m \simeq 20~$K which resembles that observed in the $c$-axis microwave conductivity. The electronic part of the longitudinal and the transverse thermal conductivity show the scaling behavior for transport properties predicted for d-wave superconductors in the temperature range $\sim 18~$K~$\le T \le 30~$K.

cond-mat.supr-con↗

arXiv2000

Magnetic-Field-Driven Superconductor-Insulator-Type Transition in Graphite

A magnetic-field-driven transition from metallic- to semiconducting-type behavior in the basal-plane resistance takes place in highly oriented pyrolytic graphite at a field $H_c \sim 1~$kOe applied along the hexagonal c-axis. The analysis of the data reveals a striking similarity between this transition and that measured in thin-film superconductors and Si MOSFET's. However, in contrast to those materials, the transition in graphite is observable at almost two orders of magnitude higher temperatures.

cond-mat.str-el↗

arXiv2000

Vortex Lattice Depinning vs. Vortex Lattice Melting: a pinning-based explanation of the equilibrium magnetization jump

In this communication we argue that the Vortex Lattice Melting scenario fails to explain several key experimental results published in the literature. From a careful analysis of these results we conclude that the Flux Line Lattice (FLL) does not melt along a material- and sample-dependent boundary $H_j(T)$ but the opposite, it de-couples from the superconducting matrix becoming more ordered. When the FLL depinning is sharp, the difference between the equilibrium magnetization $M_{eq}(T,H)$ of the pinned and unpinned FLL leads to the observed step-like change $ΔM_{eq}(T,H)$. We demonstrate that the experimentally obtained $ΔM_{eq}(T,H)$ can be well accounted for by a variation of the pinning efficiency of vortices along the $H_j(T)$ boundary.

cond-mat.supr-con↗

arXiv1999

Ferromagnetic- and Superconducting-like Behavior of Graphite

We have identified ferromagnetic- and superconducting-like magnetization hysteresis loops in highly oriented pyrolytic graphite samples below and above room temperature. We also found that both behaviors are very sensitive to low-temperature -- as compared to the sample synthesis temperature -- heat treatment. The possible contribution of magnetic impurities and why these do not appear to be the reason for the observed phenomena is discussed.

cond-mat.str-el↗

arXiv1999

Effect of the sample geometry on the second magnetization peak in single crystalline Ba$_{0.63}$K$_{0.37}$BiO$_3$ thick film

Magnetization hysteresis loop $M(H)$ measurements performed on a single crystalline Ba$_{0.63}$K$_{0.37}$BiO$_3$ superconducting thick film reveal pronounced sample geometry dependence of the "second magnetization peak" (SMP), i.e. a maximum in the width of $M(H)$ occurring at the field $H_{\rm SMP}(T)$. In particular, it is found that the SMP vanishes decreasing the film dimension. We argue that the observed sample geometry dependence of the SMP cannot be accounted for by models which assume a vortex pinning enhancement as the origin of the SMP. Our results can be understood considering the thermomagnetic instability effect and/or non-uniform current distribution at $H < H_{\rm SMP}$ in large enough samples.

cond-mat.supr-con↗